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This article examined the environmental and economic prerequisites for the widespread use of dual-fuel diesel engines in the global fleet. A brief overview of the existing cycles used in marine dual-fuel diesel engines was made.. The prospects and problems of their further development were also considered. The basis of the article is the study of a possible increase in the detonation resistance of dual-fuel diesels through the use of a strong Miller cycle. The research was conducted using the software of the leading company in the field of design and engine building AVL List GmbH. As a prototype, the serial marine engine MAN 8L51/60DF was adopted, and the model is based on data obtained during three years of its operation

As one of the most common engine types in nowadays, the thermal efficiency of spark-Ignition (SI) engine is limited due to the lower compression ratio. Various technical solutions have been proposed to suppress knock and improve compression ratio of SI engines. In this paper, an new technical solution based on electromagnetic valve train (EMVT) was proposed to suppress knock of spark ignition engines, so that high compression ratio (HCR) engine (13:5) was obtained. Moreover, experimental and numerical analyses were carried out to optimize the proposed EMVT strategy. The result showed that the proposed EMVT strategies could well suppress the engine knock by reducing end-gas temperature and pressure and improving the spark-flame rate, resulting in significantly enhanced power, economic, and emission characteristics of SI engines. This study provides theoretical basis and technical approach for the development of internal combustion engines with high efficiency and high compression ratio.

The development of maritime trade has greatly promoted the development of diesel engines. However, with the increasingly serious environmental problems, more and more attention has been paid to the exhaust emissions of high-power marine diesel engines. The restrictions on SOx have been implemented globally, and the limitation of the NOx will be the next priority. This paper illustrates (a) Principle and research progress of NOx emissions-reduction technology of marine diesel engine; (b) Summary of advantages and disadvantages among various reduction technologies and their reduction effects; (c) The application effect of mainstream technology on board. Firstly, since exhaust gas recirculation (EGR) can achieve Tier-III directly from Tier-I without considering the increased fuel consumption. It is deemed as the most promising technology to reduce emissions by controlling combustion condition. However, EGR has shortcomings of excessive increase in fuel consumption and generation of waste water, which need to be solved immediately. Secondly, selective catalytic reduction (SCR) is the most effective and straightforward means to achieve Tier-III. Despite of the continuous optimization of SCR unit volume, the problem of scrap catalyst seriously limits its wide application. How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR. Thirdly, nature gas (NG) engines are capable of achieving a reduction in NOx, but in order to meet the requirements of Tier-III, it still needs to be assisted by other technologies. The emissions of hydrocarbon (HC) and CO in NG engines are huge defects that must be solved. Lastly, technologies such as the Miller cycle, Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone. These technologies can be combined with EGR, SCR and NG engines to optimize the engines’ economy and emission characteristics.

Legislations concerning emissions from heavy-duty diesel engines are becoming increasingly stringent. This requires conventional diesel combustion to be compliant using costly and sophisticated aftertreatment systems. Preferably, diesel–methanol dual-fuel is one of the suitable alternative combustion modes as it can potentially reduce the formation of nitrogen oxide and soot emissions which characterised the diesel mixing-controlled combustion. This is primarily due to the high latent heat of vaporisation and oxygen content of the methanol fuel. At high engine loads, however, the potential of diesel–methanol dual-fuel operation is constrained by the excessive combustion pressure rise rate and peak in-cylinder pressure, which limits both the engine efficiency and the percentage of methanol that can be used. For the first time, experimental studies were conducted to explore advanced combustion control strategies such as Miller cycle, exhaust gas recirculation, and intake air cooling for improving upon high load diesel–methanol dual-fuel combustion. Experiments were carried out at 1200 r/min and 18 bar indicated mean effective pressure on a single-cylinder heavy-duty diesel engine, which equipped with a high pressure common rail diesel injection, a methanol port fuel injection, and a variable valve actuation system on the intake camshaft. Results showed that the methanol energy fraction of a conventional diesel–methanol dual-fuel operation with a baseline intake valve closing timing was limited to 28%. This was due to the high combustion temperature at a high load which advanced the ignition timing of the premixed charge, resulting in high levels of pressure rise rate. The application of lower effective compression ratio and intake air temperature ( Tint) effectively decreased the compression temperature, which successfully delayed the ignition timing of the premixed charge. This allowed for a more advanced diesel injection timing to achieve improvement in the thermal efficiency and potentially enabled a higher methanol substitution ratio. Although the introduction of exhaust gas recirculation demonstrated very slight impact on the ignition timing of the premixed charge, a higher net indicated efficiency was observed due to a relatively lower local combustion temperature which reduced heat transfer loss. Moreover, the optimised diesel–methanol dual-fuel operation allowed a higher methanol energy fraction of 40% to be used at an effective compression ratio of 14.3 and Tint of 305 K and achieved the highest net indicated efficiency of 47.4%, improving by 3.7% and 2.6%, respectively, when compared to the optimised conventional diesel combustion (45.7%) and conventional diesel–methanol dual-fuel (46.2%). This improvement was accompanied with a reduction of 37% in nitrogen oxide emissions and little impact on soot emissions in comparison with the conventional diesel combustion.

It is important to understand the lean-burn combustion process of large-bore natural gas engines and influences on it in order to improve next generations of gas engines to meet the increasing requirements for high efficiencies and low emissions. The investigations in this study focus on the ignition and early flame propagation phase using optical experiments on a single-cylinder research engine, since both phases highly influence the subsequent main-combustion. Scavenged prechambers with different operating conditions and a tangential and radial nozzle alignment as well as unscavenged prechamber and direct spark plug ignition are compared. Beside the phenomenology of the ignition system itself, the interaction of the main-chamber charge motion and the ignition system is important to understand. Therefore, different valve timings (conventional timings and Miller cycle) as well as a low and high turbulence setup are subject of the study. Numerical simulations of the cold flow are used to understand the charge motion and mixture formation in the prechamber as well as in the main-chamber. The experiments depict an enhancement of the first flame propagation phase using a scavenged prechamber due to hot turbulent jets emerging from the nozzles. Furthermore, an influence of the nozzle geometry and the boundary conditions on the jet development and on the early flame propagation is observed. It is seen by the optical measurements that cycle-to-cycle variations can originate from the hot turbulent jets and its influence on the ignition of the main-chamber charge. Further, the optical measurements show that a low in-cylinder swirl and turbulence due to Miller cycle has an impact on the interaction between the in-cylinder charge motion and the jets. A comparison between high turbulence and low turbulence in-cylinder flows on the combustion is carried out. It is shown that the scavenged prechamber can compensate the lack of turbulence in the main-chamber. Hence, the scavenged prechamber enhances the flame propagation due to induced turbulence in the main-chamber and larger flame front surfaces generated by penetrating flame torches.

The energy and environmental problem have created an urgent need for compound strategies of low-speed two-stroke diesel engines to meet stringent emission regulations. In this study, the effects of Miller cycle, exhaust gas recirculation (EGR) and intake air humidification coupled with fuel injection strategies on the engine performance at 75% load were investigated using CFD software CONVERGE. The simulated results agree with the experimental data, demonstrating that Miller cycle reduces NOx emissions significantly. Additionally, a 30% EGR alone could reduce NOx emissions to 2.519 g/kWh. And NOx emissions were decreased with increased water concentration, with a 2:1 water-to-fuel mass ratio yielding an emissions reduction of 21.4% relative to the reference case. Furthermore, dilution effect of a water addition strategy on engine performance and emission is more significant than thermal or chemical effects; moreover, H2-generated rate curve confirm the minimal influence of chemical reactions. An optimal emission reduction strategy was determined to be the M5E25W2.0P9injP900, as it was proven to satisfy Tier III emission requirements and improve the trade-off between NOx emissions and indicated specific fuel consumption. The results of this study can be used to establish a strategy to satisfy IMO Tier III requirements and avoid high fuel consumption.

In theory, high compression ratio has the potential to improve the thermal efficiency and promote the power output of the SI engine. However, the application of high compression ratio is substantially limited by the knock in practical working process. The objective of this work is to comprehensively investigate the application of high compression ratio on a gasoline engine based on the Miller cycle with boost pressure and split injection. In this work, the specific optimum strategies for CR10 and CR12 were experimentally investigated respectively on a single cylinder DISI engine. It was found that a high level of Miller cycle with a higher boost pressure could be used in CR12 to achieve an effective compression ratio similar to CR10, which could eliminate the knock limits at a high compression ratio and high load. To verify the advantages of the high compression ratio, the fuel economy and power performance of CR10 and CR12 were compared at full and partial loads. The result revealed that, compared with CR10, a similar power performance and a reduced fuel consumption of CR12 at full load could be achieved by using the strong Miller cycle and split injection. At partial load, the conditions of CR12 had very superior fuel economy and power performance compared to those of CR10.

The Miller cycle with EIVC is applied to a medium-speed marine diesel engine to achieve high-efficiency combustion and low nitrogen oxide (NOx) emissions. The effects of Miller cycle on the state parameters, combustion characteristics, NO emissions, and the spatial distribution of working fluid were analyzed. A one-dimensional (1D) simulation model was established by using the BOOST software. The FIRE software was used to simulate the combustion process and emission characteristics of the diesel engine at medium and low loads. The results show that in the E3 cycle (four kinds of loads, 100%, 75%, 50%, 25%, according to Marine application propeller law), with the proper EIVC, the in-cylinder pressure, temperature and NO emission will be reduced. At the load of 50%, NO emissions were reduced by 17.8%, At 25% load NO emissions were reduced by 14.9%. During the fuel injection, the decrease of in-cylinder temperature causes a longer ignition delay period. When the EIVC is too early, the heat release rate increases sharply, at the same time, the NO generation also increases. Furthermore, it will lead to misfire at low load.

In recent years, marine engine manufacturers have become increasingly interested in gas engines as an alternative to diesel engines to address rising crude oil prices and environmental regulations. In this study, a 1.6 MW dedicated gas engine was developed based on a diesel engine with bore 220, stroke 300. The developed gas engine had a precombustion chamber and exhibited excellent performance, the brake mean effective pressure was 2.1 MPa at 1000 rpm and NOx emissions were 50 ppm under 15% O2. In particular, it demonstrated excellent fuel economy with a thermal efficiency of 45%, and its carbon dioxide emissions were ~75% of the conventional diesel engines, thus demonstrating greenhouse gas reduction. These results indicate that suitably developed gas engines can provide a low-cost and energy-efficient alternative to diesel engines.

The introduction of innovative spark ignition engines featuring extreme downsizing, high compression ratio and Miller Cycle has led to an increasing interest in water injection as one of the most promising countermeasures to reduce the knock risk. In this paper, the potential of a Port Water Injection (PWI) system integrated in a state-of-the-art turbocharged downsized spark ignition engine was investigated through both numerical simulations and experiments. A 3D-CFD water spray model, properly calibrated against experimental data, was used to predict water spray evaporation and to evaluate the engine oil dilution risk. On the basis of the 3D CFD analysis, two new indexes were specifically defined and correlated with experimental data to evaluate the effectiveness of water injection in terms of knock mitigation and the risk of engine oil dilution. After assessing their reliability by means of a sensitivity analysis on both calibration parameters and hardware configurations, the proposed indexes were successfully exploited to perform a preliminary design and optimization of the water injection system.

A major issue nowadays that concerns the pollution of the environment is the emissions emerging from heavy-duty internal combustion engines. Such concern is dictated by the fact that the electrification of heavy-duty transport still remains quite challenging due to limitations associated with mileage, charging speed and payload. Further improvements in the performance and emission characteristics of conventional heavy-duty diesel engines are required. One of a few feasible approaches to simultaneously improve the performance and emission characteristics of a diesel engine is to convert it to operate on Miller cycle. Therefore, this study was divided into two stages, the first stage was the simulation of a heavy-duty turbocharged diesel engine (4-stroke, 6-cylinder and 390 kW) to generate data that will represent the reference model. The second stage was the application of Miller cycle to the conventional diesel engine by changing the degrees of intake valve closure and compressor pressure ratio. Both stages have been implemented through the specialist software which was able to simulate and represent a diesel engine based on performance and emissions data. An objective of this extensive investigation was to develop several models in order to compare their emissions and performances and design a Miller cycle engine with an ultimate goal to optimize diesel engine for improved performance and reduced emissions. This study demonstrates that Miller cycle diesel engines could overtake conventional diesel engines for the reduced exhaust gas emissions at the same or even better level of performance. This study shows that, due to the dependence of engine performance on complex multi-parametric operation, only one model achieved the objectives of the study, more specifically, engine power and torque were increased by 5.5%, whilst nitrogen oxides and particulate matter were decreased by 30.2% and 5.5%, respectively, with negligible change in specific fuel consumption and CO2, as average values over the whole range of engine operating regimes.

Because of the late intake valve closure (LIVC), Miller cycle is kind of low temperature cycle which means it has the ability to refrain the knocking and produce higher thermal efficiency effectively in engines. As kind of clean energy and whose combustion products are perfectly environmental-friendly, ethanol has been considering as an ideal fuel substitution for a long time. Therefore in order to reduce NOx and other particulates emissions from engine, this paper presented the technical route which applied Miller cycle and ethanol to a turbocharged diesel engine. The simulation results shown that, Miller cycle did bring considerable improvements on reducing NOx emission in a certain extent. Comparing with the conventional Diesel cycle NOx emission value has been reduced in the range of 8.5–12.9% by applying Miller cycle. After applying turbocharger into Miller cycle engine model, NOx emission was slightly raised mostly back to the same figure as Diesel cycle produced. Moreover, taking ethanol as fuel also produced large reduction on NOx emission comparing with the conventional engine model which taking diesel as fuel, and the range of reduction was 5.2–8.5% which could be considered as a considerable improvement. However, when turbocharger added under the same situation the figure of the range of reduction was 4.53–5.16% which is slightly lower than without turbocharger. As for particulate emission in the engine, the situation which Miller cycle and turbocharger caused was opposite to the result of NOx emission that both Miller cycle and turbo-charged Miller cycle caused a larger amount of particulate emission probably due to the higher burning temperature.

Miller cycle has been shown as a promising engine strategy to reduce in-cylinder nitrogen oxide (NOx) formation during the combustion process and facilitate its removal in the aftertreatment systems by increasing the exhaust gas temperature. However, the level of NOx reduction and the increase in exhaust gas temperature achieved by Miller cycle alone is limited. Therefore, research was carried out to investigate the combined use of Miller cycle with other advanced combustion control strategies in order to minimise the NOx emissions and the total cost of ownership. In this article, the effects of Miller cycle, exhaust gas recirculation, and post-injection were studied and analysed on the performance and exhaust emissions of a single cylinder heavy-duty diesel engine. A cost–benefit analysis was carried out using the corrected total fluid efficiency, which includes the estimated urea solution consumption in the NOx aftertreatment system as well as the fuel consumption. The experiments were performed at a low load of 6 bar net indicated mean effective pressure. The results showed that the application of a Miller cycle–only strategy with a retarded intake valve closing at −95 crank angle degree after top dead centre decreased NOx emissions by 21% to 6.0 g/kW h and increased exhaust gas temperature by 30% to 633 K when compared to the baseline engine operation. This was attributed to a reduction in compressed gas temperature by the lower effective compression ratio and the in-cylinder mass trapped due to the retarded intake valve closing. These improvements, however, were accompanied by a fuel-efficiency penalty of 1%. A further reduction in the level of NOx from 6.0 to 3.0 g/kW h was achieved through the addition of exhaust gas recirculation, but soot emissions were more than doubled to 0.022 g/kW h. The introduction of a post-injection was found to counteract this effect, resulting in simultaneous low NOx and soot emissions of 2.5 and 0.012 g/kW h, respectively. When taking into account the urea consumption, the combined use of Miller cycle, exhaust gas recirculation, and post-injection combustion control strategies were found to have relatively higher corrected total fluid efficiency than the baseline case. Thus, the combined ‘Miller cycle + exhaust gas recirculation + post-injection’ strategy was the most effective means of achieving simultaneous low exhaust emissions, high exhaust gas temperature, and increased corrected total fluid efficiency.

The Miller cycle has been proven to be an effective way to improve the thermal efficiency for gasoline engines. However, it may show insufficient power performance at certain loads. In this study, the objective is to exploit the advantages of the Miller-cycle engines over the original Otto-cycle engines. Therefore, a new camshaft profile with early intake valve closure was devised, and two various pistons were redesigned to obtain higher compression ratio 11.2 and 12.1, based on the original engine with compression ratio 10. Then, a detailed comparative investigation of the effects of Miller cycle combined with higher compression ratio on the performance and emission of a turbocharged gasoline direct injection engine has been experimentally carried out based on the engine bench at full and partial loads, compared to the original engine. The results show that, at full load, for a turbocharged gasoline direct injection engine utilizing the Miller cycle, partial maximum power is compromised about 1.5% while fuel consumption shows a strong correlation with engine speed. At partial load, since the Miller effect can well reduce the pumping mean effective pressure, thus improves the fuel economy effectively. In addition, the suppression of the in-cylinder combustion temperature induced by the lower effective compression ratio contributes to the reduction of nitrogen oxide emission greatly. However, the total hydrocarbon emission increases slightly. Therefore, a combination of the Miller cycle and highly boosted turbocharger shows great potential in further improvement of fuel economy and anti-knock performance for downsized gasoline direct injection engines.

This paper establishes an air-standard irreversible Dual-Miller cycle (DMC) model with the specific heat ratio (SHR) of working fluid (WF) linearly varying with its temperature. Because the specific heat (SH) of WF varies with combustion reaction in actual internal combustion engine (ICE), the SHR of WF should be a function of temperature but not a constant. In order to accurately reflect the practical characteristics of DMC engine, performance of DMC with linearly variable SHR, and with heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses (IILs) is analyzed and optimized by applying finite-time thermodynamics. Analytical formulae of the power output ( P ), efficiency ( η ), entropy generation rate (EGR) and ecological function ( E ) are derived. Relationships among P , η , E and compression ratio are obtained via numerical calculations. Effects of the design parameters, cycle temperatures and linearly variable SHR of WF on P , η and E are investigated. Performance differences among the DMC and its simplified cycles, including Otto cycle (OC), Dual cycle (DDC) and Miller cycle (OMC) are compared. Performance characteristics of the DMC with different optimization objective functions (OOFs) are analyzed. The results indicate that the maximum power output ( MP ), maximum efficiency ( MEF ) and maximum ecological function ( ME ) of the DMC are superior to those of OC, DDC and OMC, and optimizing E is the best compromise between optimizing P and optimizing η . The presented results may be helpful to optimize the performance of practical DMC engines.

In-cylinder charge density at top dead center is an important parameter of diesel engines and is influenced by intake pressure, intake temperature, and compression ratio. The effects of charge density on fuel spray, combustion process, and emissions were investigated by using a constant volume bomb and a heavy-duty diesel engine. Spray development resistance increased with the increase of the charge density in the constant volume bomb. It was found that short spray penetration was accompanied by a large spray cone angle in the former stage with high charge density. However, the equivalence ratio was lowered and the degree of homogeneity of the mixture was increased in the later stage owing to the rapid interaction of fuel and gas at a high mixing rate. Combining the first law of thermodynamics and the second law of thermodynamics for analysis, as the charge density increased, the gross indicated thermal efficiency (ITEg) was improved. However, pumping loss had to be considered with higher charge density. Under this condition, the brake thermal efficiency (BTE) trend was increased initially and decreased subsequently. Under high-load operation (1200 r/min BMEP, 2.0 MPa), the minimum charge density value of 44.8 kg/m3 was found to be reasonable. This charge density was suitable for combustion and brought about minimum exhaust energy and trade-off emissions. Moreover, by analyzing two operation conditions in terms of the maximum BTE with the Miller and the conventional cycles, compression temperature and combustion temperature were reduced in the Miller cycle with the charge density 44.8 kg/m3. A high Cp/Cv could improve the cylinder exergy/power conversion process by its positive effect of increasing the specific heat ratio. Owing to the interaction between a high Cp/Cv and exergy loss to heat transfer, the condition with the minimal charge density could produce more piston work.

This paper establishes an irreversible Dual-Miller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal ρopt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P, η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P, η and E are derived. The relationships among P, η, E and compression ratio (e) are obtained by numerical examples. The effects of ρ and rM on P, η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P, η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twice-maximum efficiency, and a twice-maximum ecological function, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2%of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in η compared to choosing as the optimization objective.

International audience; The Miller cycle, using an early inlet valve closing, can significantly improve the overall efficiency of a spark ignition engine during partial load operations. The shorter valve intake event minimizes the need for throttling the air and so reduces the pumping losses. This method is known as “dethrottling”. Indeed, the use of a variable valve lift system makes it possible to combine two different cam profiles in an engine, one for the full load operations and one for the partial loads. The benefits of this strategy, combined with a variable valve timing (VVT) system, will be explored using a new 0D model. This model can take into account the strong changes of in-cylinder turbulence generated by the VVT and their effects on the combustion. Efforts have been made to reduce the model's reliance on external inputs. Therefore, analytical calculations of quantities, such as the flame radius, have been favored. The Miller cycle can lead to indicated efficiencies around 44% and the addition of a VVT system can improve the overall efficiency up to 1% over a wide range of engine loads.

This paper describes the development of an aggressive Miller cycle gasoline engine with stoichiometric combustion, a high expansion ratio of 12.5:1, a 65 crank angle degrees (CAD) longer duration Late-Intake-Valve-Closing (LIVC) cam, and a two-stage turbocharger. The full-load performance and part-load fuel consumption of the baseline and Miller cycle engines were assessed through engine dynamometer testing. The aggressive Miller cycle engine achieved the maximum Brake Mean Effective Pressure (BMEP) of 22 bar at 1500 rpm, which was enabled by the 65 CAD longer duration LIVC cam to further reduce the effective compression for controlling knock and by the two-stage turbocharger to provide significantly higher boost for maintaining and increasing trapped mass. It was shown that the more aggressive Millerization was realized while maintaining the specific output and advantages of current downsized boosted engines, such as lower friction and lower pumping losses. The aggressive Miller cycle engine achieved above 6% brake-specific fuel consumption (BSFC) reduction over the baseline turbocharged spark-ignition engine on average. The 65 CAD longer duration LIVC cam provided the benefit of pumping loss reduction with delayed intake valve closing and the benefit of hot residual dilution with relatively advanced intake cam phasing simultaneously, which provided the significant fuel economy improvement at non-knocking light-load conditions. Even without the latest technology enhancements and friction reduction methods on its base engine hardware, the aggressive Miller cycle engine achieved a very broad BSFC island of 230 g/kWh or lower, with the lowest BSFC of 223 g/kWh at 2000 rpm and 10 bar BMEP.

The pre-turbine steam injection and the Miller cycle can be combined together to improve engine performances, but matching strategies of those two approaches under different operating conditions still need to be clarified. In this paper, thermodynamic processes of the pre-turbine steam injection and the Miller cycle are studied first followed by matching strategies based on a non-dimensional matching map. Experiments are also conducted to show merits of this new system applied on a turbocharged diesel engine. The results show that the steam mass flow rate has a much bigger effect on air supplying characteristics of the turbocharger than the steam temperature, while the Miller cycle degree shows a big influence on the air consuming characteristics of the engine. With the steam/exhaust gas mass flow ratio of 0.1, the fuel economy under full load conditions can be improved by up to 5.9% at 1500 rpm. At the rated speed of 2100 rpm, the fuel economy deteriorates by 1.3% with the steam injection but can be improved by 2.8% further combined with the Miller cycle. Thus, different matching strategies of those two approaches should be adopted under different engine conditions.

This study reports a new model of an air standard Dual-Miller cycle (DMC) with two polytropic processes and heat transfer loss. The two reversible adiabatic processes which could not be realized in practice are replaced with two polytropic processes in order to more accurately reflect the practical working performance. The heat transfer loss is taken into account. The expressions of power output, thermal efficiency, entropy generation rate (EGR) and ecological function are addressed using finite-time thermodynamic theory. Through numerical calculations, the influences of compression ratio, cut-off ratio and polytropic exponent on the performance are thermodynamically analyzed. The model can be simplified to other cycle models under specific conditions, which means the results have an certain universality and may be helpful in the design of practical heat engines. It is shown that the entropy generation minimization does not always lead to the best system performance.

The conventional Diesel cycles engine is now approaching the practical limits of efficiency. The recuperated split cycle engine is an alternative cycle with the potential to achieve higher efficiencies than could be achieved using a conventional engine cycle. In a split cycle engine, the compression and combustion strokes are performed in separate chambers. This enables direct cooling of the compression cylinder reducing compression work, intra cycle heat recovery and low heat rejection expansion. Previously reported analysis has shown that brake efficiencies approaching 60% are attainable, representing a 33% improvement over current advanced heavy duty diesel engine. However, the achievement of complete, stable, compression ignited combustion has remained elusive to date. The challenge is to induct hot high pressure charge air close to top dead centre into the combustion cylinder and then inject and burn the fuel before the piston has travelled significantly down the expansion stroke. In this paper, we report results from a single cylinder split cycle combustion research engine. Stable, rapid combustion was achieved at 800 rpm and 1200 rpm at the retarded timings required for a split cycle engine. The calculated rate of heat release was more rapid than typically observed on conventional compression ignition engine suggesting good mixing of the fuel and air during induction. One dimensional cycle analysis was used to calculate the implications of the test results on the full engine cycle which indicated class leading brake efficiencies approaching and possibly exceeding, 60% are possible from a split cycle engine.

The diesel engine is an indispensable part of technology and it is commonly used in land and marine vehicles. However, diesel engines release NOx emissions due to high combustion temperatures. They have harmful effects on the environment such as sources of photo-chemical fog and climate changes. Therefore, they must be reduced and limited. The Miller cycle application is a NOx control method and it is popular in the recent years to abate NOx produced from the internal combustion engines (ICEs). A performance investigation of a Dual-Miller cycle (DMC) engine in terms of power (PO), power density (PD) and effective efficiency (EE) has been performed using a new finite-time thermodynamics modeling (FTTM) in this study. The effects of engine design and operating parameters on the engine performance (EPER) have been examined. Additionally, the energy losses have been determined resulting from incomplete combustion (IC), friction (FR), heat transfer (HT) and exhaust output (EO). The results presented could be an essential tool for DMC marine engine designers.

[EN] Different air management strategies, Miller timing and internal EGR (iEGR), have been studied on internal combustion engines with the objective of decreasing NOx emissions. This paper explores heavy duty diesel engine performance by the application of both strategies separately through two different camshaft configurations, mounted and tested in the same engine. On one side, in the case of Miller timing, the early intake valve closing is explored, and on other side, for iEGR, the study is carried out opening the exhaust valve during the intake process. The engine emission and performance study is achieved through the application of a methodology which begins with the selection of the operating points focusing on medium to high loads. It continues with the exploration of different camshaft profiles by mean of a 1D model. Through the 1D model, two camshaft profiles are selected and tested in the test cell, determining the intake valve closing conditions followed by the identification of the thermodynamic behavior during the compression stroke before the injection. Later on, the combustion and emissions formation analysis is performed to conclude with the fuel consumption study for each implemented strategy taking into consideration the important influence of each camshaft profile in the pumping loop. A short discussion on the transient performance effect of each air management strategy completes the scope of the study., Daniel Estepa is partially supported through contract FPI-S2-2015-1091 of Programa de Apoyo para la Investigacion y Desarrollo (PAID) of Universitat Politecnica de Valencia.

A full cycle computational fluid dynamics (CFD) simulation model has been established to study the effect of injection direction and exhaust valve close (EVC) timing on performance and emissions for a slow speed marine engine. In order to find more combustion details, the model was coupled with simplified chemical kinetics mechanism. Meanwhile the paper presents the optimization results combining variable injection direction with late exhaust valve closing (LEVC). The results indicate that the consistency of injection direction and flow direction has an important impact on fuel economy. To improve fuel consumption, the injection direction must be carefully adjusted within certain limits. A certain degree of sacrifice in fuel economy is reflected on the transient calculation using the LEVC strategy. However, significant improvement in NOx (nitrogen oxides) emission can be achieved accordingly. With optimized EVC timing and injection direction, lower NOx emission can be realized with no penalty of fuel consumption.

In this study, experiments were conducted to improve the thermal efficiency by increasing the geometric compression ratio (GCR) to obtain higher expansion ratio, and using late intake valve closing (LIVC) Miller cycle to keep the effective compression ratio (ECR) within knock limit, in a stoichiometric operation natural gas engine with exhaust gas recirculation (EGR). The results indicate that, in a wide range of operating conditions, since the necessary exhaust gas recirculation dilution level leads to a large spark advance, the effective compression level around the spark timing has large difference and weak correlation with the effective compression ratio; in this case, the effect of the retarded intake valve closure (IVC) timing on lowering the compression temperature around the spark timing becomes much more significant; in addition, the increased geometric compression ratio could result in higher heat transfer loss around top dead center (TDC) due to the increased surface/volume (S/V) ratio. Consequently, even the effective compression ratio can be restored or further increased with higher geometric compression ratio compared to the baseline, the combustion rate is inevitably lowered or hardly increased. As engine speed and load increase, the adverse effect of the retarded intake valve closure timing on combustion rate could be further enhanced, mainly due to the increased cooling effect of the introduced and expelled charge on the cylinder wall. Through the thermodynamic analysis, it is observed that the adverse effect of the increased effective compression ratio on heat transfer loss is much more obvious compared to its positive effect on combustion rate, even within knock limit. All these factors restrict the thermal efficiency improvement potential obtained by the increased expansion ratio with higher geometric compression ratio. Finally, the net indicated thermal efficiency (ITEn) can be improved by nearly 2% at each tested operating condition with the optimization.

In this research, a second order sliding mode (SOSM) strategy to control the Atkinson cycle engine breathing subsystem with an alternative late intake valve closing (LIVC) scheme is presented. The control framework based on extended mean value engine model (EMVEM) of the Atkinson cycle engine in view of fuel economy is evaluated for the standard Federal Urban Driving Schedule (FUDS) and US06 driving cycles. In this context, the authors have already proposed a control-oriented EMVEM model of the Atkinson cycle engine with variable intake valve actuation, well suited for SOSM design. To demonstrate the benefits of the VCR Atkinson cycle engine over conventional Otto cycle engine, in the presence of auxiliary loads and uncertain road loads, its EMVEM model is simulated by using a precisely tuned super-twisting controller having similar specifications as that of the conventional gasoline engine. The resulting approach confirms the significant decline in engine part load losses and improvement in the thermal efficiency and, accordingly, exhibits considerable enhancement in the fuel economy of the VCR Atkinson cycle engine over Otto cycle engine during the wide operating range.

With the ever so imminent threat of climate change caused by man-made pollution, IMO introduces a new piece of legislature: IMO Annex 6 Tier III regarding air pollution. To meet new standards of exhaust air content, engineers are scrambling to find new and efficient ways to keep the shipping industry going. With the dawn of two-stage turbocharging developing high values of inlet air pressure in combination with early IVC using variable valve actuation depending on the engine load, the regulations are met. In this study the effectiveness of the previously mentioned concepts are put to the test against the conventional Diesel cycle used on board most vessels today. A detailed comparison of the two is conducted followed by a thorough analysis and argumentation.

The new emission legislation for sea-going vessels issued by the International Maritime Organization (IMO) requires drastic reduction in exhaust gas nitrogen oxides (NOx), and the combination of different primary methods can be an interesting solution without increasing remarkably the machinery. In this paper, the Miller cycle and the dilution with exhaust gas in the combustion chamber were tested to reach the Tier III limits for a four-stroke marine engine. In particular, the Miller cycle is used to reduce the in-cylinder temperature, and lower oxygen content in the combustion chamber is realized with cooled exhaust gas recirculation (EGR). Despite a remarkable reduction in NOx, the main drawback was a significant increase in fuel consumption. Split injection is combined with the abovementioned methods, in order to improve the engine efficiency. The novelty of this study consists in the simultaneous use of a split fuel injection, the Miller cycle and EGR in a marine-size application. Along this study, combining Miller timing with a relatively low EGR rate reduces NOx emissions by 90%. On the other hand, split injection does not bring significant advantages in fuel economy, although the results with very early pilot injection suggest further studies to be realized.

The influence of Miller cycle and variable geometry turbocharger (VGT) on combustion and emissions was investigated in steady and transient operation of a heavy-duty diesel engine. The experiment was conducted on a six-cylinder diesel engine with common rail fuel injection, two-stage turbocharger and Miller cycle. The results revealed that Miller cycle decreased soot and nitrogen oxides (NOx) emissions and increased brake thermal efficiency (BTE) in certain operation. In the steady operation, the intake flow was reduced in a cold condition because the low oil temperature led to the hydraulic mechanism delay intake valve closing timing. However, by adjusting VGT, low emissions of soot and NOx could still be obtained with relatively high BTE. In cold transient process, dynamic response of torque depended on indicated work and gas pumping work. A good trade-off performance could be achieved by maintaining the initial VGT rack position for 0.5 s. Compared to VGT variation under the steady-state map, soot peak emissions were reduced by 50% with NOx emissions nearly unchanged by VGT control strategy 3 and Miller cycle. Compared to diesel conventional cycle, the combination of Miller cycle and VGT control strategy 3 can not only ensure quick dynamic torque response, but also reduce NOx peak emissions by 10% with slightly increased soot peak emissions.

In this study, application of the steam injection method (SIM), Miller cycle (MC) and turbo charging (TC) techniques into a four stroke, direct-injection diesel engine has been numerically and empirically conducted. NOx emissions have detrimental influences on the environment and living beings. They are formed at the high temperatures, thus the Diesel engines are serious NOx generation sources since they have higher compression ratios and higher combustion temperatures. The international regulations have decreased the emission limits due to environmental reasons. The Miller cycle (MC) application and steam injection method (SIM) have been popular to abate NOx produced from the internal combustion engines (ICEs), in the recent years. However, the MC application can cause a reduction in power output. The most known technique which maximizes the engine power and abates exhaust emissions is TC. Therefore, if these three techniques are combined, the power loss can be tolerated and pollutant emissions can be minimized. While the application of the MC and SIM causes to diminish in the brake power and brake thermal efficiency of the engine up to 6.5% and 10%, the TC increases the brake power and brake thermal efficiency of the engine up to 18% and 12%. The experimental and theoretical results have been compared in terms of the torque, the specific fuel consumption (SFC), the brake power and the brake thermal efficiency. The results acquired from theoretical modeling have been validated with empirical data with less than 7% maximum error. The results showed that developed combination can increase the engine performance and the method can be easily applied to the Diesel engines.

This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine bench test, the effects with the Miller cycle application under 3000 rpm were studied. The results show that the Miller cycle has different extents of improvement on pumping loss, combustion and friction loss. For low, medium and high loads, the brake thermal efficiency of the baseline engine is increased by 2.8%, 2.5% and 2.6%, respectively. Besides, the baseline variable valve timing (VVT) is optimized by the test. Subsequently, the 1D CFD (Computational Fluid Dynamics) model of the Miller cycle engine after the test optimization at the working condition of 3000 rpm and BMEP (Brake Mean Effective Pressure) = 10 bar was established, and the influence of the combined change of intake and exhaust valve timing on Miller cycle was studied by simulation. The results show that as the effect of the Miller cycle deepens, the engine’s knocking tendency decreases, so the ignition timing can be further advanced, and the economy of the engine can be improved. Compared with the brake thermal efficiency of the baseline engine, the final result after simulation optimization is increased from 34.6% to 35.6%, which is an improvement of 2.9%.

High nitrogen oxide levels of the conventional diesel engine combustion often requires the introduction of exhaust gas recirculation at high engine loads. This can adversely affect the smoke emissions and fuel conversion efficiency associated with a reduction of the in-cylinder air-fuel ratio (lambda). In addition, low exhaust gas temperatures at low engine loads reduce the effectiveness of aftertreatment systems necessary to meet stringent emissions regulations. These are some of the main issues encountered by current heady-duty diesel engines. In this work, variable valve actuation–based advanced combustion control strategies have been researched as means of improving upon the engine exhaust temperature, emissions, and efficiency. Experimental analysis was carried out on a single-cylinder heady-duty diesel engine equipped with a high-pressure common-rail fuel injection system, a high-pressure loop cooled exhaust gas recirculation, and a variable valve actuation system. The variable valve actuation system enables a late intake valve closing and a second intake valve opening during the exhaust stroke. The results showed that Miller cycle was an effective technology for exhaust temperature management of low engine load operations, increasing the exhaust gas temperature by 40 °C and 75 °C when running engine at 2.2 and 6 bar net indicated mean effective pressure, respectively. However, Miller cycle adversely effected carbon monoxide and unburned hydrocarbon emissions at a light load of 2.2 bar indicated mean effective pressure. This could be overcome when combining Miller cycle with a second intake valve opening strategy due to the formation of a relatively hotter in-cylinder charge induced by the presence of internal exhaust gas recirculation. This strategy also led to a significant reduction in soot emissions by 82% when compared with the baseline engine operation. Alternatively, the use of external exhaust gas recirculation and post injection on a Miller cycle operation decreased high nitrogen oxide emissions by 67% at a part load of 6 bar indicated mean effective pressure. This contributed to a reduction of 2.2% in the total fluid consumption, which takes into account the urea consumption in aftertreatment system. At a high engine load of 17 bar indicated mean effective pressure, a highly boosted Miller cycle strategy with exhaust gas recirculation increased the fuel conversion efficiency by 1.5% while reducing the total fluid consumption by 5.4%. The overall results demonstrated that advanced variable valve actuation–based combustion control strategies can control the exhaust gas temperature and engine-out emissions at low engine loads as well as improve upon the fuel conversion efficiency and total fluid consumption at high engine loads, potentially reducing the engine operational costs.

In order to explore the technical route to meet the Tier III emission regulations, the experimental study of the influence of Miller cycle combined with EGR on the performance, energy and exergy of a four-stroke marine regulated two-stage turbocharged diesel engine was achieved by redesigning the camshaft and EGR system. The results shown that Miller cycle combined with EGR increased the peak HRR of premixed combustion period, decreased the peak HRR during the main combustion period, and delayed the crank angle corresponding to the peak HRR, resulting in longer combustion duration and a later 50% combustion position. In the 75% load, the combination of medium Miller timing and medium EGR rate can not only meet the NOx emission requirements of Tier III, but also far superior to only high EGR rate in terms of fuel economy, opacity performance and COVIMEP. As the EGR rate increased, heat transfer energy to coolant, BTE and ITE dropped significantly, while exhaust energy and combustion loss increased significantly. The change trends of exergy terms with EGR rate and Miller timing were similar to their corresponding energy. It should be noted that the exhaust energy was about 2.5 times larger than the exhaust exergy while the heat transfer energy to coolant was about 8 times larger than the heat transfer exergy to coolant, which indicated that the recoverable potential of heat transfer energy to coolant is much smaller than exhaust energy.

In order to further improve thermal efficiency and fuel economy, the engine community pays more attention to the advanced controlling strategy. In this paper, the impacts of the continuous variable valve lift (CVVL) system and Miller cycle strategy on the performance behavior of the natural gas spark ignition (SI) engine were comprehensively investigated. The results indicated that pumping loss was decreased, and volumetric efficiency slightly increased with using CVVL. In addition, the intake air mass flow at the intake ports became more smooth, and turbulence flow and its intensity were strengthened with using CVVL, which were beneficial to accelerate combustion rate and improve combustion efficiency. Under the partial load of the 1200 rpm 5 bar, the ratio of the pumping mean effective pressure (PMEP) in indicated mean effective pressure (IMEP) was reduced by 2.74%. Furthermore, an extra 5.43% improvement of indicated thermal efficiency was obtained. On the other hand, peak in-cylinder pressure and peak combustion temperature of the natural gas SI engine operated on Miller cycle were decreased with late intake valve close (LIVC), particularly the pressure and temperature at the end of the compression stroke, which resulted in reducing NOx emissions formation and mitigating knocking combustion. However, the intake mass flow at the intake ports became fluctuation and the volumetric efficiency was decreased with using LIVC. In addition, brake specific fuel consumption was increased and indicated thermal efficiency decreased with employing LIVC.

In order to analyze and improve the thermodynamic process of marine diesel engines and improve energy efficiency, the experimental study of the influence of Miller timing on the performance, energy and exergy of marine diesel engines was realized by redesigning the camshaft and adjusting the two-stage turbocharging system. The research results shown that with the increase of Miller timing, the average pumping loss decreased, the peak HRR and the maximum combustion temperature decreased, and the crank angle corresponding to the peak HRR was delayed backward, resulting in a backward delay of the 50% point, the 10–90% combustion duration was extended, and the EER, EEE and BTE first increased and then decreased. Secondly, the Miller cycle combined with two-stage turbocharging could make marine diesel engines reduced NOx emissions by more than 25% with a small effect on the BSFC. In addition, as the Miller timing increased, the proportion of exhaust energy, heat transfer energy to coolant, mechanical loss, and combustion loss all decreased, while the proportion of brake output work first increased and then decreased. The change trends of exergy terms with load and Miller timing were similar to their corresponding energy. It was worth noting that the exhaust exergy accounted for about 40% of the exhaust energy, while the heat transfer exergy to coolant accounted for only 13% of the heat transfer energy to coolant, indicating that the exhaust energy quality was higher, the utilization potential was greater, and the efficient utilization interval was concentrated in the high load area.

Previous studies have shown that increase compression ratio (CR) is an effective way to improve thermal efficiency of gasoline engine without changing the mechanical structure and working cycle, however, it is limited by engine knock when increasing the intake boosting under high load operation. This study aimed to solve the knock problem of gasoline engine with higher CR by application of Miller cycle, which can be implemented by either early or late intake valve closing (EIVC or LIVC). Therefore, in this paper, based on the engine with CR of 13.5 and electromagnetic valves train (EMVT), a comparative study was carried out to investigate the effects of EIVC and LIVC on engine performance, by theoretical modeling and calculation. The results show that, at high load, EIVC strategy is more preferred than LIVC owing to its lower total power consumption, which can improve the indicated mean effective pressure (IMEP) by 0.0371 bar, while enhance turbulence intensity and improve combustion. And at part load, the advantage for EIVC declines gradually, nevertheless, it can still sensitively adjust the EGR rate and thus reduce NOx. This results of quantitative analysis about two Miller cycles can provide valuable reference for engine designers and researchers.

In this work, a computational fluid dynamic model is established based on a natural gas engine and experimental results, and the combustion system of stoichiometric operation natural gas engine (intake manifolds and combustion chambers) is optimized based on knocking boundary extension under high load condition. In addition, the effects of Miller cycle and EGR on the combustion and knocking boundary extension are also explored. Results reveal that the intensity and distribution of in-cylinder turbulent kinetic energy will significantly affect the flame development and combustion characteristics. The combination of spiral intake manifold + K15 chamber shows better performance in antiknock because of the enhanced in-cylinder airflow motion and flame development. In addition, the Miller cycle with the late intake valve close timing of 20 °CA can effectively extend the antiknock performance of the engine under the current operating operation. EGR has limited effect on turbulent kinetic energy, and the primary affective mechanism of EGR on knocking is mainly achieved by changing the in-cylinder temperature during the combustion process. It is found that with tangential and spiral intake manifold + K15 chamber, combined with late intake valve closing (20 °CA) and EGR (30%), the indicated mean effective pressure (IMEP) can be increased by 5.21% within the knocking boundary compared to that of the original combustion system.

[EN] Passive pre-chamber ignition concept has been proven to be an excellent strategy to increase the ignition energy and enhance the combustion velocity even when spark-ignition engines are operating in diluted conditions. Other benefits of this system are the increased combustion stability and combustion efficiency, reducing hydrocarbons and carbon monoxide emissions. However, these advantages are limited at some operation conditions such as low engine load or diluted conditions since both the energy available in the pre-chamber and the scavenge of combustion products are compromised. In this framework, numerical studies using two different computational tools, based on one-dimensional modeling, are utilized to gain knowledge about the governing parameters and to improve the design of a pre-chamber when the engine operates at these restrictive conditions. In particular, the impact of the pre-chamber volume, the total cross sectional area of the holes and tangential angle of the nozzles have been numerically evaluated. Different pre-chamber designs were proposed and experimentally tested in a single-cylinder, high compression ratio turbocharged spark-ignition engine fueled with compressed natural gas and operating on Miller cycle. Results give valuable insight into the key aspects of the internal geometry and some relevant design paths to follow for a suitable pre-chamber definition., The work has been partially supported by the Spanish Ministerio de Economia y Competitividad through Grant No. TRA2017-89139-C2-1-R. P.J. Martinez-Hernandiz is partially supported by an FPI contract (FPI-S2-19-21993) of the "Programa de Apoyo para la Investigacion y Desarrollo (PAID-05-19)" of the Universitat Politecnica de Valencia.

The Magma engine concept is characterised by a high compression ratio, central injector combustion system employed in a downsized direct-injection gasoline engine. An advanced boosting system and Miller cycle intake-valve closing strategies are used to control combustion knock while maintaining specific performance. A key feature of the Magma concept is the use of high CR without compromise to mainstream full-load performance levels.

This paper describes the design optimization of a compound boosting system consisting of a turbocharger and a supercharger for a 2.0 l four-cylinder Miller cycle engine which has a high expansion ratio of 12.0:1 and variable valve actuation. Various system configurations and supercharger sizes were evaluated numerically and experimentally to reduce the supercharger power consumption and the engine fuel consumption while maintaining the same engine torque performance in steady-state conditions. The supercharger–turbocharger boosting system with a V400 supercharger showed an average engine fuel consumption that was 2.8% lower in boosted conditions than did the turbocharger–supercharger boosting system with the same V400 supercharger; this was predicted by engine cycle simulations and verified by experiments. When the supercharger was placed upstream of the turbocharger, the supercharger inlet pressure was lower and the total mass flow rate through the supercharger was reduced, which reduced the supercharger power consumption and the bypass air flow. The turbocharger–supercharger boosting system with a smaller supercharger (R340 or V250) significantly improved the engine efficiency (by 3.3% or 5.0% respectively in comparison with the turbocharger–supercharger boosting system with a V400 supercharger), by reducing the mass air flow rates through the supercharger and minimizing the supercharger power consumption. The turbocharger–supercharger boosting system with a V250 supercharger achieved the lowest engine fuel consumption in full-load conditions of all the turbocharger and supercharger compound boosting system options evaluated for the 2.0 l Miller cycle engine on the basis of the simulation results. This study defined the optimal system layout and the optimal supercharger size for implementing the turbocharger and supercharger compound boosting system on a 2.0 l Miller cycle spark ignition engine to maximize the improvement in the fuel economy of the vehicle while maintaining the same torque performance.

In this paper, an ecological-based numerical analysis and optimization have been carried out for an air-standard irreversible Dual-Miller cycle engine with late inlet valve closing version using the ecological coefficient of performance (ECOP) criterion which covers finite rate of heat transfer, heat leak and internal irreversibilities. A detailed computational analysis has been performed in order to examine the general and optimum performances of the cycle. The results obtained based on ECOP function are compared with a different ecological function and with the maximum power output conditions. The consequences of ECOP, ecological function and maximum power output conditions are acquired based on the compression ratio, cut-off ratio, pressure ratio, Miller cycle ratio, source temperature ratio and internal irreversibility parameter. The influences of these parameters on the optimum performances are examined in detail.

It has been well known that the engine downsizing combined with intake boosting is an effective way to improve the fuel conversion efficiency without penalizing the engine torque performance. However, the potential of engine downsizing is not yet fully explored, and the major hurdles include the knocking combustion and the pre-turbine temperature limit, owing to the aggressive intake boosting. Using the engine cycle simulation, this paper compares the effects of the Miller and five stroke cycles on the performance of the deeply downsized and highly boosted SI engine, taking the engine knock and pre-turbine temperature into consideration. In the simulation, the downsizing is implemented by reducing the combustion cylinder number from four to two, while a two stage boosting system is designed for the deeply downsized engine to ensure the wide-open-throttle (WOT) performance comparable to the original four cylinder engine. The Miller cycle is realized by varying the intake valve timing and lift, while the five stroke cycle is enabled with addition of an extra expansion cylinder between the two combustion cylinders. After calibration and validation of the engine cycle simulation models using the experimental data in the original engine, the performances of the deeply downsized engines with both the Miller and five stroke cycles are numerically studied. For the most frequently operated points on the torque-speed map, at low loads the Miller cycle exhibits superior performance over the five-stroke cycle in terms of fuel conversion efficiency, while at higher loads the thermal efficiency of the five stroke cycle, owing primarily to elimination of fuel enrichment operations, is higher than that of the Miller cycle engine. For the WOT operation, even with the two-stage boosting system, at the engine speed below 1700 rpm the deeply downsized engine with the Miller cycle fails to deliver the torque comparable to the original engine, while the targeted WOT torque can be achieved with the five stroke cycle engine at all the engine speeds but 800 rpm. The mechanism of the efficiency differences between the Miller and five stroke cycles is discussed in depth with the energy balance and influencing factor analysis on thermal efficiency.

Hydrogen is a promising energy carrier, and the port fuel injection (PFI) is a fuel-flexible, durable, and relatively cheap method of energy conversion. However, the contradiction of increasing the power density and controlling NOx emissions limits the wide application of PFI hydrogen internal combustion engines. To address this issue, two typical thermodynamic cycles—the Miller and Otto cycles—are studied based on the calculation model proposed in this study. The thermodynamic cycle analyses of the two cycles are compared and results show that the thermal efficiency of the Miller cycle (ηMiller) is higher than ηOtto, when the multiplied result of the inlet pressure and Miller cycle coefficient (δMγM) is larger than that of the Otto cycle (i.e., the value of the inlet pressure ratio multiplied by the Miller cycle coefficient is larger than the value of the inlet pressure ratio of the Otto cycle). The results also show that the intake valve closure (IVC) of the Miller cycle is limited by the inlet pressure and valve lift. The two factors show the boundaries of the Miller cycle in increasing the power density of the turbocharged PFI hydrogen engine. The ways of lean burn + Otto cycle (LO), stoichiometric equivalence ratio burn + EGR + Otto cycle (SEO) and Miller cycle in turbocharged hydrogen engine are compared, the results show that the Miller cycle has the highest power density and the lowest BSFC among the three methods at an engine speed of 2800 rpm and NOx emissions below 100 ppm. The brake power of the Miller cycle increases by 37.7% higher than that of the LO and 26.3% higher than that of SEO, when γM is 0.7. The BSFC of the Miller cycle decreases by 16% lower than that of the LO and 22% lower than that of SEO. However, the advantage of the Miller cycle decreases with an increase in engine speed. These findings can be used as guidelines in developing turbocharged PFI hydrogen engines with the Miller cycle and indicate the boundaries for the development of new hydrogen engines.

In this paper, the development of a Miller cycle gasoline engine which has a high compression ratio from 11.5:1 to 12.5:1, single-stage turbocharging and external cooled exhaust gas recirculation is described. The improvement in the fuel economy by adding external cooled exhaust gas recirculation to the Miller cycle engine at different geometric compression ratios were experimentally evaluated in part-load operating conditions. The potential of adding external cooled exhaust gas recirculation in full-load conditions to mitigate pre-ignition in order to allow higher geometric compression ratios to be utilized was also assessed. An average of 3.2% additional improvement in the fuel economy was achieved by adding external cooled exhaust gas recirculation to the Miller cycle engine at a geometric compression ratio of 11.5:1. It was also demonstrated that the fuel consumption of the engine with external cooled exhaust gas recirculation was reduced by 3–7% in a wide range of part-load operating conditions and that the engine output of the Miller cycle engine at a geometric compression ratio of 12.5:1 increased at 2000 r/min in the full-load condition. The Miller cycle engine with external cooled exhaust gas recirculation at a geometric compression ratio of 12.5:1 achieved a broad brake specific fuel consumption range of 220 g/kW h or lower, with the lowest brake specific fuel consumption of 215 g/kW h. While there are still challenges in implementing external cooled exhaust gas recirculation, the Miller cycle engine with single-stage turbocharging and external cooled exhaust gas recirculation showed its potential for substantial improvement in the fuel economy as one of the technical pathways to meet future requirements in reducing carbon dioxide emissions.

In order to improve the thermal efficiency of engines, it is essential to increase their geometric compression ratio or the expansion ratio. This research explores the technology options to enable a higher expansion ratio in future boosted spark-ignition direct-injection engines, with the aim of significantly reducing the fuel consumption while achieving the same torque and combustion performances as those of baseline turbocharged engines. Variable-valve-actuation technologies such as the late-intake-valve-closing cam strategy and the early-intake-valve-closing cam strategy were considered, and their effectiveness in reducing the effective compression and preventing knock in high-compression-ratio engines was assessed. To compensate for the torque loss due to late intake valve closing or early intake valve closing, multi-stage boosting systems including the turbocharger–supercharger combination and the two-stage turbocharger were implemented and compared. In this study, a Miller cycle engine concept with a high expansion ratio of 12.0:1 was developed with variable valve actuation and multi-stage boosting. On the basis of this new concept, an engine was built and extensively tested on an engine dynamometer to assess its part-load fuel consumption and full-load performance. The experimental results indicated that this engine concept can improve the fuel economy of the vehicle by 3–4% at typical city and highway driving conditions while maintaining the same performance.

Miller cycle is applied to improve performance and emission characteristics of a gas engine. There are different types of Miller cycle concept utilization through variation of valve timing either by early intake valve closure or late intake valve closure. In this study finite-volume method is used to analyse the performance and emission characteristics of a four-stroke 12-cylinder turbocharged Miller cycle gas engine. Therefore, experimental data are used to calibrate the results derived from 3D combustion simulation and 1D overall engine simulation. The Miller cycle application shows that about 30 CAD (crank angle degrees) advancement of IVC compared with standard cycle reduces emissions such as NOx to half its magnitude. However, a little reduction in power output seems inevitable. Also, compression ratio reduction contributes to almost 15% decrease in maximum in–cylinder pressure. Moreover, retardation of IVC simultaneously improves performance and emission characteristics. However, no significant change of in–cylinder peak pressure and temperature is seen.

In this paper, comparative performance analyses of the irreversible OMCE (Otto Miller cycle engine), DiMCE (Diesel Miller cycle engine) and DMCE (Dual Miller cycle engine) based on the MP (maximum dimensionless power) output, MPD (maximum dimensionless power density) and MEF (maximum thermal efficiency) criteria have been performed by taking irreversibility due to irreversible-adiabatic compression and expansion processes into account. The maximum values of the thermal efficiency, dimensionless power output and dimensionless power density are obtained depending on pressure ratio, stroke ratio, cut-off ratio, miller cycle ratio, exhaust temperature ratio, cycle temperature ratio and cycle pressure ratio and the isentropic efficiencies of irreversible-adiabatic processes. The engine design parameters at the MP, MPD and MEF conditions are determined and their variations are investigated with respect to miller cycle ratio.

In this paper, a full-factorial design of experiment was applied to thoroughly investigate the effects of compression ratio, intake valve closing retardation angle, and engine speed on the fuel consumption performance and power performance of the Miller cycle engine based on a quasi-dimensional simulation model. A new indirect analysis method based on formula derivation and main effect analysis was proposed to simplify the complex relationship between the design factors and the performance parameters. The definition of effective compression ratio was modified to take account of the actual mass of mixture trapped in the cylinder. The results show that the distributions of brake mean effective pressure and brake specific fuel consumption can be regarded as the re-organization results from the distributions of volumetric efficiency and indicated efficiency. The intake valve closing retardation angle has a strong negative correlation with volumetric efficiency. The modified effective compression ratio is the approximate product of the compression ratio and the volumetric efficiency, and makes obvious effects on the distribution of the indicated efficiency. Therefore the combustion process is co-evolved with the intake process in a Miller cycle engine. The further improvement of brake specific fuel consumption is mainly limited by four factors, i.e., the back flow loss, the exergy loss, the incomplete expansion loss, and the combustion loss. The improvement of fuel consumption performance is at a cost of power performance, and the trade-off between the both essentially results from the knock constraint. The engine speed makes obviously effects on both volumetric efficiency and indicated efficiency, resulting in increasing the nonlinearity of the variation of the performance parameters. However, the nonlinearity provides a possibility for a Miller cycle range extender to improve the fuel consumption performance and power performance at same time by optimizing the controlled speed.

This paper reports ecological performance analyses and optimization of irreversible gas cycle engines such as Joule–Brayton cycle (JB), Atkinson cycle (AC), Otto cycle (OC), Diesel cycle (DC), Miller cycle (MC), Dual-Atkinson cycle (DAC), Dual-Diesel cycle (DDC), Dual-Miller cycle (DMC) engines based on the ecological coefficient of performance (ECOP) criterion which covers internal irreversibility, heat leak and finite-rate of heat transfer. Comprehensive computational analyses have been conducted to investigate the global and optimal performances of the gas cycle engines. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been acquired introducing the compression ratio, cut-off ratio, pressure ratio, air recharging ratio, source temperature ratio and internal irreversibility parameter. The changes of cycle performances with respect to these parameters are examined and demonstrated with figures.