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Using a combined energy cycle based on conventional and/ or clean energy sources can be a suitable option to dominate the limitations in the field of energy. Meanwhile, the select of the prime power source in such processes is a challengeable issue. The selection of the prime power source from renewable sources and in addition the use of system waste heat can lead to enhance power generation. In the present work, an energy system based on conventional energy sources and clean technology is introduced and investigated. The new integrated hybrid energy cycle is composed of Miller cycle engine (MC), alkaline fuel cell (AFC), alkaline electrolyzer, Organic Rankine cycle (ORC) system and Stirling engine. MC and AFC are used as the main power sources of the cycle. On the other hand, ORC and Stirling engine for generating more electricity from the waste heat of the cycle are applied. The electrolyzer embedded in the cycle receives its electricity from the MC and provides the required inputs of the AFC. Although many studies had been done on the integration of various power generation sources with different energy cycles, attempts had not been done to establish a study on the hybrid of MC, AFC, alkaline electrolyzer, Stirling engine and ORC to produce additional electricity. Results revealed that the introduced energy system generates 3.75 kW of electric power. The portion of MC, fuel cell, ORC, and Stirling engine in electric power production is 71.2, 10.8, 9.5 and 8.5%, respectively. However, the alkaline electrolyzer consumes 2.06 kW of power and generates 48.2 g/h of H 2 fuel. It was also found that the cycle exergy destruction is 3.34 kW. In addition, the use of MC and AFC heat dissipation heat can enhance power generation.

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.

Annotation. Introduction. Currently, the issue of fuel efficiency, emissions regulation of harmful substances and the search for alternative fuels is especially relevant. The choice of natural gas for an engine as an alternative to traditional fuels imposes its limitations, which can be avoided by applying the Miller cycle. The purpose of the study was to determine and compare the potential for improving 6ChN13/15 diesel engine converted for an energy efficient duel-fuel engine operating according to the Miller cycle with early closing of the intake valve and the engine potential of Otto thermodynamic cycle. Methodology and research methods . The research was carried out by a natural experiment method. Scientific novelty and results . A comparative analysis of various experimental results studies of engines thermodynamic cycles running on natural gas has been carried out. The results obtained will be used to create and further optimize a duel-fuel engine by controlling its workflow and the air supply system. Practical significance . The indicators results of Otto engines and engines operating according to Miller's thermodynamic cycles with early closing of the intake valve have been compared. The results obtained may be of interest to truck manufacturers and engine specialists.

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.

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.

Many methods have been developed to reduce emissions from marine heavy-fuel oil (HFO) engines. The effects of exhaust gas recirculation (EGR), Miller cycle, humid air motor (HAM), and start...

The rapid growth in automotive industry and increased fuel consumption and environmental pollution, along with decrease in oil and fossil fuel resources, necessitate the adoption of new technologies to improve engine thermal efficiency and the use of alternative fuels. So, the present study proposes the thermodynamic cycle model of engine based on the Miller cycle and the use of bioethanol and diesel fuels. To analyze the cycle performance after examining the thermodynamic processes of the Miller cycle in the pressure diagram in terms of volume and calculating the amount of the operating fluid (fuel) and its thermodynamic properties based on bioethanol and diesel fuels and a homogeneous mixture of air, temperature was determined at the key points of engine operation through thermodynamic relationships. Then, the changes of engine performance parameters including output power and thermal efficiency were compared in terms of compression ratio based on Miller cycle using bioethanol and diesel fuels and they were also compared to the Otto cycle. The results showed that by increasing density ratio, the output power and thermal efficiency first increase and then decrease. Assuming to have the same volumetric efficiency and use bioethanol fuel, the engine output power and thermal efficiency would increase. Under optimum conditions of engine performance, power at the maximum point of efficiency and efficiency at the maximum point of power in the Miller cycle were greater than those of the Otto cycle. The results can be generalized to Atkinson cycle and other alternative fuels and used in a more practical way in the design and performance evaluation of internal combustion engines.

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.

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.

[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.

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.

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.

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.

Currently, the internal combustion engine is facing tough regulations regarding pollution and CO2. In order to comply with the latest constraints concerning the CO2 emission, the automotive manufacturers must increase the thermal efficiency of the combustion engine. One way which seems to be preferential for the manufacturers is to implement the Miller over-expanded cycle. One drawback of this cycle is that the flow inside the cylinders is steadier than in the case of the Otto cycle. Consequently, in the present study, in order to understand the air flow phenomena inside the cylinder, a 3D CFD simulation is used. The weight of the study is on the understanding of the internal aerodynamics in the case of the Miller cycle. Finally, solutions to improve the situation were also given.

Exhaust gas recirculation (EGR) can be widely used to reduce the oxynitride (NOx) pollution in Low-Speed Two-Stroke Marine Diesel Engines. In this paper, two EGR systems (HP EGR 1 and LP EGR 2 ) were investigated in terms of the influence of different rates on the brake specific fuel consumption (BSFC) and the NOx emissions. As for this simulation, the exhaust gas cleaning water treatment was not concluded. Besides, Miller Cycle was used to determine the influence of its valve timing on BSFC and NOx emissions. The combination of Miller Cycle and HP EGR system decreased the NOx emissions, which could meet the IMO 3 Tier III standard, 3.4 g/kWh. Moreover, the influence of the EGR cooling temperature was discussed. Finally, a fuzzy comprehensive evaluation model was developed to evaluate the two EGR systems. The results showed that when the HP EGR system and the LP EGR system were all operating at a maximum EGR rate, LP EGR system showed more advantages.

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.

The simulation model of two-stroke heave fuel oil marine diesel engine was developed in this paper. The model was validated with the experimental data. The ability of NOx reduction was researched for exhaust gas recirculation, humid air motor and miller cycle based on the simulation model. The results show that the EGR has the most potential to reduce the NOx emission. It can make the quantity of NOx meet the requirement of Tier Ⅲ. The reduction value of NOx was less for miller cycle. The HAM can be reduced the NOx. However, the depth of HAM was limited.

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.

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.

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.

Este trabalho tem por objetivo analisar o desempenho de um motor operando em modo mono combustível com óleo diesel (OD) e em modo bicombustível, utilizando como combustível primário o gás natural (GN) e como secundário, a injeção piloto de OD. No modo bicombustível de funcionamento, o GN é admitido junto com o ar de combustão, sendo a mistura comprimida e entra em combustão após a ignição do OD injetado. O motor estudado é de seis cilindros em linha, ciclo Diesel e turboalimentado. Os ensaios de desempenho (torque, potência, consumo específico de combustível e emissões gasosas) do motor mencionado foram realizados em um banco dinamométrico, cujo freio (retarder) é do tipo eletromagnético arrefecido a ar. Os dados obtidos dos ensaios foram corrigidos de acordo com a norma NBR ISO 3046/1. Um primeiro conjunto de ensaios foi realizado para avaliar o desempenho do motor operando somente com óleo OD. As tendências das curvas de torque, potência e consumo específico de combustível pela rotação do motor foram similares àquelas correspondentes do fabricante, mas, quantitativamente, os valores ficaram aquém. Os experimentos em modo bicombustível (OD-GNV) foram realizados a 1800 RPM e se conseguiu um percentual de substituição do óleo diesel de quase 73%, representando uma redução nos custos com combustíveis, especialmente de OD, de quase 29%. Com o maior percentual de substituição de OD também houve o maior rendimento térmico do motor (31,1%) em comparação ao modo OD100 (25,6%).

Miller timing is one of the promising ways which can improve the fuel consumption of internal combustion engines. Indeed, Miller timing employing an early intake valve close is widely applied to large diesel and gas engines to enhance performance and reduce NOx emissions. In this study, performance evaluation is carried out by 1-D cycle simulation in order to estimate the effect of Miller CAM timing before BDC for a 32 L turbocharged diesel engine. To optimize Miller CAM timing, a single stage turbocharger is matched with an early intake valve close since boost pressure is a significant parameter that can control compression work in a turbocharged engine. The engine simulation result shows that there is enough potential to improve fuel consumption rate and also reduce NOx emissions at the same time.Abstract here.

In this paper, the first and second-laws efficiencies are applied to performance analysis of an irreversible Miller cycle. In the irreversible cycle, the linear relation between the specific heat of the working fluid and its temperature, the internal irreversibility described using the compression and expansion efficiencies, the friction loss computed according to the mean velocity of the piston and the heat-transfer loss are considered. The effects of various design parameters, such as the minimum and maximum temperatures of the working fluid and the compression ratio on the power output and the first and second-laws efficiencies of the cycle are discussed. In the following, a procedure named ANN is used for predicting the thermal efficiency values versus the compression ratio, and the minimum and maximum temperatures of the Miller cycle. Nowadays, Miller cycle is widely used in the automotive industry and the obtained results of this study will provide some significant theoretical grounds for the design optimization of the Miller cycle.

Performance improvement in power generation systems have been current issues in the recent years. Combined power plants including Organic Rankine Cycle are promising for performance improvement to generate efficient energy. This study has examined a way of optimum conditions for both efficiency and exhaust emissions by introducing a combined plant of Dual Miller Cycle-Organic Rankine Cycle focused on diesel engine applications. Three different types of working fluids with appropriate characters are used in the Organic Rankine Cycle. Effective efficiency, effective power, exergy destruction, effective power density, ecological coefficient of performance, exergetic efficiency and effective ecological power density are investigated for both Dual Miller Cycle and Dual Miller Cycle – Organic Rankine Cycle combined plant configurations. The impacts of engine design and working parameters such as cycle temperature ratio, cycle pressure ratio, engine speed, cylinder dimensions and equivalence ratio on the performance parameters are investigated. Octafluorocyclobutane and pentafluoropropane have been used as working fluids of Organic Rankine Cycle. The results showed that pentafluoropropane is the best suitable organic fluid. The effective efficiency, ecological coefficient of performance and exergy destruction have been found as 45.42%, 74.14% and 12.4 kW, respectively. The results of this examination have shown optimum values of the engine design and operating parameters in terms of thermo-ecological feasibility which also reduces harmful ship emissions like nitrous oxides.

A one-dimensional thermodynamic simulation model was built based on the test data and using the system dynamics method to study the effects of geometric compression ratio, late intake valve closing (LIVC), air fuel ratio, exhaust gas recirculation (EGR) and ignition advance on the thermal efficiency of a straight line 6 cylinder miller cycle natural gas engine. The result shows that improve engine geometry compression ratio appropriately can effectively improve engine energy distribution, engine power and fuel economy. And compared with LIVC setting, ignition advance setting has a more obvious effect on engine performance. Proper ignition advance ensures high efficiency of the engine. Moderately increasing EGR rate can effectively guarantee the low NOx emission, and further increase LIVC can reduce exhaust gas dilution effect on inhibition of engine combustion rate, to ensure that the engine has good thermal efficiency.

[EN] The low temperature, premixed combustion strategies are being investigated in the recent years as a mean to break the NOx-soot trade-off appearing during the diffusive conventional diesel combustion. This approach relies on promoting premixed combustion events with shortened duration, which reduces the heat transfer losses, improves the thermal efficiency, and allows a simultaneous reduction of engine-out NOx and soot emissions. However, since the combustion onset only depends on chemical kinetics, most of these strategies cannot be implemented at medium and high loads due to excessive pressure gradients, which lead to unacceptable noise levels and reliability issues. This experimental work investigates the potential of the Miller cycle as a strategy to minimize the aforementioned challenges when operating under reactivity controlled compression ignition combustion. Moreover, the coupled effect of the Miller cycle with the fuel reactivity modulation is also explored as a way for improving the combustion control. For this purpose, parametric studies varying the effective compression ratio and gasoline fraction have been done in a single-cylinder heavy-duty engine operating at 14 bar indicated mean effective pressure and 1200 rev/min as a baseline condition. The results show that this strategy allows better control of the in-cylinder thermodynamic conditions, enabling a simultaneous reduction of nitrogen oxides and soot emissions down to the EURO VI limits, while keeping a reduced fuel consumption and suitable in-cylinder maximum pressure gradients., The authors thanks VOLVO Group Trucks Technology for supporting this research. The authors also acknowledge the Spanish economy and competitiveness ministry for partially supporting this research (HiReCo TRA2014-58870-R). 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.

The Atkinson cycle provides the potential to increase the efficiency of SI engines using overexpansion concept. This also will suggest decrease in CO2 generation by internal combustion engine. In this study a mathematical modeling of complete thermodynamic cycle of a new two-stroke Atkinson cycle SI engine will be presented. The mathematical modeling is carried out using two-zone combustion analysis in order to make the model predict exhaust emission so that its values could be compared with the values of conventional SI engine. The model also is validated against experimental tests in that increase in efficiency is achieved compared to conventional SI engines.