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Variable valve timing (VVT) and Miller cycle are advanced technologies employed to optimize engine performance by improving airflow exchange, which are seldom investigated based on the direct-injection (DI) hydrogen engine. The objective of this study is to assess the effects of intake valve closing (IVC) and exhaust valve opening (EVO) timing on the gas exchange performance, combustion, and emissions of a DI hydrogen engine, after which a synergistic control strategy of IVC and EVO timing is proposed. This work is conducted under wide-open throttle and 1500 rpm. The results indicate that the synergistic control of IVC and EVO timing can increase volumetric efficiency by more than 40%, enhance gas exchange performance, shorten combustion duration, and reduce cyclic variation, resulting in approximately 43.15% brake thermal efficiency. Furthermore, brake mean effective pressure can be increased by more than 60% and NO emissions are controlled to less than 20 ppm by optimizing valve timings. • A synergistic control strategy of intake and exhaust VVT is proposed. • The airflow exchange and combustion of a DI hydrogen engine are optimized. • The regulation of valve timings can improve gas exchange performance. • The engine can reach 43.15% maximum brake thermal efficiency. [ABSTRACT FROM AUTHOR]

Aiming to further improve the thermal efficiency and reduce NO x emissions in the stoichiometric hydrogen-enriched natural gas (NG) engine, a detailed 3-D simulation model of stoichiometric operation heavy-duty NG engine is built based on the actual boundary conditions from high load bench test. The superimposed methods for knock regulation, combustion and emission control, including Miller valve timing, hydrogen volume fraction and EGR rate were proposed and investigated comprehensively. It reveals that the typically bimodal characteristic of heat release rate (HRR) curve is caused by knock, which seriously restricts the performance improvement of stoichiometric NG engine under high load condition. To predict and control the occurrence of the second peak of HHR accurately, a new parameter BI is defined. Moreover, the Miller timing with 20°CA of the intake valve late closing shows better combustion performance within the knock limit, accompanied by a slight increase in NO x emissions. Additionally, the 5% hydrogen blend, coupled with the Miller cycle, can further enhance the indicated thermal efficiency (ITE) of the NG engine due to the stronger effects on acceleration of laminar flame propagation velocity than the promotion of end-gas auto-ignition. Besides, the great potential of EGR rate for balancing NO x and ITE is also confirmed in the heavy-duty hydrogen-enriched NG engine adopting Miller cycle. Compared to the original indexes, combing with the regulation strategies of intake valve late closing (20°CA), hydrogen addition (5%) and EGR (17%) are proved to increase the indicated thermal efficiency by 1.89% and reduce NO x emissions by 11.47% within the knock limit. • The superimposed effects of Miller cycle, hydrogen addition and EGR rate on knock, combustion and emission are explored. • A new parameter is proposed for predicting and controlling the occurrence of the second peak of HRR due to knock. • The potential of hydrogen addition in improving thermal efficiency considering the knock is investigated. • Higher EGR ratio within the knock limitation can effectively suppress NO X emissions and improve thermal efficiency. [ABSTRACT FROM AUTHOR]

• The valve timing controlling strategies are analyzed experimentally over the whole operating map. • A multi-indicator decision-making method is applied to analyze the weight of BTE and NOx emissions. • Advanced intake and exhaust valve timings are employed to enhance the BTE at medium–low loads. • Retarded exhaust valve timing helps reduce NOx emissions at high loads. • A maximum power of 124.8 kW and a BTE of 42.57 % is achieved with optimized VVT. The direct-injection hydrogen engine (DI-H 2 ICE) has demonstrated zero carbon emissions with high brake thermal efficiencies (BTE). Due to the high stoichiometric air–fuel ratio of hydrogen, with a lean burn strategy the gas exchange process of a hydrogen engine is different to a gasoline engine, and the valve timing controlling strategy requires reinvestigation. In this research, the optimal variable valve timing (VVT) is investigated in a 2.0 L DI H 2 ICE. The intake and exhaust valve timing controlling strategies are analyzed experimentally over the whole operating map. A multi-indicator decision-making method is applied to determine the entropy weight of BTE and NOx emissions. Results indicate that BTE greatly benefits from advanced intake valve timing, and exhaust valve timing affects BTE through pumping losses. Advanced intake and exhaust valve timings are employed in the hydrogen engine to enhance the BTE until the NOx emissions rise rapidly at high loads. The retarded exhaust valve timing helps reduce NOx emissions and avoid the risk of abnormal combustion at high loads. Therefore, earlier IVO and later EVC are applied simultaneously for DI-H 2 ICE compared to the gasoline engine. A maximum power of 124.8 kW at an engine speed of 4500 rpm and a BTE of 42.57 % is achieved with optimized VVT. Furthermore, NOx emissions are controlled to under 20 ppm over nearly half of the engine operating map. The conclusions are valuable in the development of high-performance H 2 ICEs, the numerical simulation studies, and hydrogen fuel applications. [ABSTRACT FROM AUTHOR]

The Miller cycle has significant advantages of suppressing knocking and improving nitrogen oxide (NO X) emissions without the penalties of reducing engine fuel consumption and power output. In the study, the effect of non-Miller cycle and Miller cycle on the exhaust gas recirculation (EGR) introduction capability and the knocking boundary were evaluated on a stoichiometric combustion natural gas engine at three different loads. Additionally, the effect of Miller cycle coupled EGR and ignition timing on engine performance and combustion process was discussed. The results indicate that, for the same condition, the Miller cycle could reduce peak temperature and pressure, increased combustion duration, and delayed combustion phase, which makes for effective knocking suppression. Therefore, the Miller cycle has less dependence on the EGR strategy to control knock. Moreover, the Miller cycle can also reduce the ability to introduce EGR, which could up to 3.8%. By matching the ignition timing and EGR rate, the BSFC of the Miller cycle were decreased by 0.6g/kW·h, 2.4 g/kW·h and 2.9 g/kW·h respectively for three test conditions compared with non-Miller cycle. In terms of emissions, the Miller cycle and EGR can both suppress NO X emissions, while the EGR being more effective. The study will provide valid information for the application of the Miller cycle to achieve efficiency clean combustion of natural gas engine. • The effect of different cycles on the boundary parameters of the engine is compared. • The effect of the Miller cycle on the combustion process of the engine is investigated. • The potential for optimizing fuel economy and improving NO X emissions of Miller cycle coupled EGR is explored. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To achieve low-carbon transportation, a novel Miller cycle was implemented by using asynchronous late intake valve closing (ALIVC) in the high compression ratio turbocharged SI engine. The effects of the Miller cycle on combustion and performance were investigated and compared with the original Otto cycle. Based on this, EGR was introduced and its effects on Miller cycle engine performance and energy balance were investigated. The results show that the Miller-CR12.5 can reduce pumping loss and suppress knock without sacrificing power output. Compared to the Otto-CR10.5, the Miller-CR12.5 achieves a 6.7 % reduction in BSFC at the lowest fuel consumption point and a 10–11.4 % reduction at high loads. The lower peak combustion temperature allows the Miller-CR12.5 to eliminate fuel-enriched injection at high loads, reducing the heat transfer and combustion loss. The introduction of EGR in the ALIVC Miller cycle engine decreases the peak HRR and extends the combustion duration. However, the advanced 50 % combustion position and increased effective expansion ratio can improve engine performance. At 10 % EGR rate, the BSFC obtains a 2.1 % reduction and NOx emissions are reduced by 62 %. As the EGR rate increases, the heat transfer and exhaust loss decrease, but there is a slight increase in combustion loss. • A novel Miller cycle was achieved by using asynchronous late intake valve closing. • ALIVC Miller cycle significantly improves engine performance. • ALIVC Miller cycle can fully eliminate fuel-enrichment injection at high loads. • Optimized BSFC and NOx emissions through Miller cycle combined with EGR. [ABSTRACT FROM AUTHOR]

Abstract The Miller cycle with EIVC is applied to a medium-speed marine diesel engine to achieve high-efficiency combustion and low nitrogen oxide (NO x) 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. Graphical abstract Image 1 Highlights • The BOOST model was established for the medium-speed marine diesel engine with four-stroke and 6 cylinders. • The accuracy of the calculated model was verified at 25%, 50% loads of E3 cycle. • The combustion process and emission characteristics were investigated by 3D CFD software. • The best EIVC varies with different loads. [ABSTRACT FROM AUTHOR]

Abstract 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 NO x 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 NO x emission. It can make the quantity of NO x meet the requirement of Tier Ⅲ. The reduction value of NO x was less for miller cycle. The HAM can be reduced the NO x. However, the depth of HAM was limited. [ABSTRACT FROM AUTHOR]

• High compression ratio and Miller cycle effectively reduced BSFC for methanol engine. • The EIVC Miller cycle shortened the combustion duration of methanol engine. • The EIVC Miller cycle significantly reduced COV IMEP of methanol engine. Considering the excellent anti-knock property of methanol fuel and the fact that passenger car engines typically operate at medium to low loads, this paper increasing the compression ratio and adopting the Miller cycle to improve the engine's efficiency, based on a methanol engine with compression ratio of 9.5:1. Experimental research is conducted to analyze the engine's combustion and emission characteristics under different operating conditions. The research shows that increasing the compression ratio to 12:1 can effectively reduce methanol consumption under medium to low loads, and applying the Miller cycle on the compression ratio of 12:1 can further improve fuel economy at low loads. Increasing the compression ratio raises the engine's cylinder pressure, maximum pressure rise rate, and cycle-to-cycle variation, thereby enhancing the tendency for knocking. However, the Miller cycle can effectively alleviate this situation while reducing engine pumping losses. From the perspective of emissions at medium and low loads, the high compression ratio reduces CO and HC emissions but increases NOx emissions due to high combustion temperature. The Miller cycle's shorter combustion duration and lower combustion temperature result in higher CO and HC emissions compared to an Otto cycle at the same compression ratio, but NOx emissions are improved. [ABSTRACT FROM AUTHOR]

Based on a single-cylinder engine modified from a heavy-duty compression ignition engine with gasoline compression ignition (GCI), the influences of (i) delaying the intake valve closing timing (IVCT), (ii) a two-pulse fuel injection strategy and (iii) the injection pressure on combustion and emissions under high-load conditions are studied. By delaying the IVCT, the effective compression ratio and cylinder temperature during the compression stroke can be reduced, which can increase the fuel ignition delay and reduce soot emission and the heat-transfer loss rate, contributing to expand the engine’s high-load limit for high efficiency and clean combustion. With IVCT delay at an inlet pressure of 3.0 bar and a gross indicated mean effective pressure (IMEPg) of 16.5 bar, the gross indicated thermal efficiency (ITEg) is 52.3%, which increases by 2.4% compared to the case without IVCT delay. Combining IVCT delay, two-pulse injection, and an appropriate injection pressure can reduce the fuel mixing time, which can decrease the ringing intensity (RI) and achieve clean combustion at high engine load. Using IVCT delay, an intake pressure of 3.4 bar, an exhaust-gas recirculation (EGR) rate of 47%, a pilot injection of 10% at (−70, −7), an injection pressure of 80 MPa, and an IMEPg of 15 bar, the ITEg is 53.1% and the emissions of soot and NOx are 0.0068 g/kWh and 0.21 g/kWh, respectively. [ABSTRACT FROM AUTHOR]

Downsizing a spark ignition (SI) engine with boost pressure is a proven way of increasing the thermal efficiency and reducing CO 2 emissions. However, the occurrence of abnormal combustion problems such as knock and super knock could seriously damage the downsized SI engine and limit its efficiency improvement. In this study, the effects of the Miller cycle on anti-knock and engine power are experimentally investigated using a single-cylinder gasoline engine, the speed corresponded to 1600 rpm and air–fuel ratio corresponded to 1. The Miller cycle provides a good anti-knock performance because of its low in-cylinder temperature induced by the lower effective compression ratio, however, it has a poor dynamic output. To increase the intake charge of the Miller cycle, boost pressure was applied. The results showed a clear improvement in both the thermal efficiency and torque of the engine. Furthermore, the knock tendency of the engine was reduced. However, compared with the Miller cycle without boost pressure, the knock tendency with boost pressure was significantly higher. Therefore, to improve both engine power and knock resistance, this study combined split injection to the Miller cycle with boost pressure. The result indicates that the combined method can effectively decrease the knock tendency and increase the engine torque. The best secondary start of injection timing for the Miller cycle with boost pressure and split injection is 100 CAD BTDC. In conclusion, the Miller cycle with intake boost pressure and split injection has a considerable potential for achieving both a better knock resistance and higher engine power. [ABSTRACT FROM AUTHOR]

At high load, dual-fuel compression ignition engines often rely on exhaust gas recirculation (EGR) to avoid excessive in-cylinder pressure rise rates caused by the autoignition of the premixed fuel. This can adversely affect the net indicated efficiency depending on the resulting fuel/air equivalence ratio and pressure differential across the cylinder used to drive the requested amounts of EGR. In this work, advanced combustion control strategies have been experimentally investigated to improve ethanol-diesel dual-fuel operation at a high engine load of 1.8 MPa net indicated mean effective pressure. Miller cycle and charge air cooling have been explored to reduce the in-cylinder gas temperature and help control the ethanol autoignition process, potentially minimising the EGR requirements and increasing net indicated efficiency. Experiments were carried out on a single-cylinder heavy-duty engine equipped with a high pressure common rail diesel injection, an ethanol port fuel injection, and a variable valve actuation system on the intake camshaft. Exhaust emissions and net indicated efficiency were measured and discussed for different ethanol energy fractions. Early autoignition of the premixed ethanol fuel at the baseline intake valve lift profile resulted in high levels of pressure rise rate, which limited the ethanol energy fraction to 0.26. The application of a Miller cycle strategy via late intake valve closing events effectively delayed the ethanol autoignition process. The reduction of the intake manifold air temperature via an air-to-water charge air cooler also suppressed the early ignition of ethanol. Both approaches allowed for a substantial improvement in terms of the maximum ethanol energy fraction, which was increased to 0.79 without EGR. Moreover, high load dual-fuel operations with Miller cycle and charge air cooling attained higher net indicated efficiency and lower nitrogen oxides emissions than conventional diesel combustion. These improvements can help generate a viable business case of dual-fuel combustion as a technology for future compression ignition engines. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia, as two renewable carbon-free combustibles, are considered to be potentially excellent alternative fuels for internal combustion engines. Since hydrogen and ammonia have opposite and complementary combustion characteristics, the co-combustion of ammonia with hydrogen is reasonable. However, there are few detailed experimental studies of load control strategies for an ammonia‑hydrogen engine. In this study, four load control strategies including the variation of ammonia volume share (AVS), qualitative control, quantitative control, and adjustment of intake variable valve timing (VVT) are proposed and assessed for their applicability in an ammonia/hydrogen dual-fuel engine. The ignition and combustion characteristics of ammonia do not allow for high thermal efficiency, so the Miller cycle is introduced to improve engine performance. The engine employs fuel supply modes of ammonia port injection and hydrogen direct injection at 1500 rpm. In general, the engine achieves higher brake mean effective pressure (BMEP) and brake thermal efficiency (BTE) at different AVS. Moreover, qualitative control and adjustment of intake VVT allow the engine to own a wide regulation range of BMEP and maintain the BTE of more than 37% under most conditions. However, quantitative control appears to be an inadequate strategy for the engine due to the lower BMEP and BTE. • The co-combustion of ammonia with hydrogen and hydrogen direct injection are crucial. • Four load control strategies are proposed for an ammonia/hydrogen dual-fuel engine. • Technologies of the Miller cycle and variable valve timing are used in the engine. • Higher cyclic variation should be avoided when using various load control strategies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ammonia-hydrogen fuel used in miller cycle internal combustion engine. • The stoichiometric and lean-burn conditions of the ammonia-hydrogen engine were compared. • For Miller Cycle ammonia engines, about 20% of hydrogen is required. • Expanded ammonia energy ratio can improve engine BMEP and ITE. Reducing carbon emissions in the transport sector requires technology upgrades to engines and the use of carbon–neutral fuels. Ammonia is a zero-carbon renewable fuel that complements hydrogen. This study is based on a Miller cycle spark ignition engine using ammonia-hydrogen fuel. The effects of the mixture ratio of ammonia and hydrogen under stoichiometric ratio and lean burn condition on the performance of the Miller cycle engine are focused. First, a commercial Miller-cycle ICE was modified to allow a dual fuel supply of ammonia and hydrogen. The engine was run steadily at 1500 rpm with the manifold absolute pressure (MAP) maintained at 60 kPa, and the ammonia and hydrogen supplies were adjusted to achieve different mixing ratios and excess air ratios. The test results showed that an increased ammonia percentage under stoichiometric ratio conditions significantly improved the Braking mean effective pressure (BMEP) and Braking thermal efficiency (BTE) of the ICE. Under lean burn conditions, the changes of BMEP and BTE are small with the increase of the ammonia ratio. The exhaust temperature of the ammonia-hydrogen engine is relatively low, so it is necessary to consider matching a small inertia turbocharger. Ammonia ratios above 80 % by volume resulted in erratic engine operation and even misfires. Ammonia-hydrogen fuel blends lead to higher Nitrogen oxide (NOx) emissions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The steam injection method (SIM) has been widespread to abate NOx of internal combustion engines (ICEs). Another NOx reduction method known in the literature is the Miller cycle (MC) application. However, this method causes a reduction in the power output. The most known technique which improves the engine power and decreases emissions is the turbo charging (TC). Hence, these three methods can be combined to make up for the power loss and to decrease pollutant emissions at higher rates. In this study, the combination of the SIM, TC and MC methods (SIM-TC-MC) has been carried out for a direct injection (DI), naturally aspirated diesel engine. The results have been compared with standard condition (STD) in terms of the engine performance and CO, CO 2 , NO, HC. Optimal condition has been determined as 10 CA retardation, 20% steam ratio of the fuel mass and 1.1 TC pressure (C62-S20-T1.1) in terms of the minimum NO formation. At this condition, NO, HC, CO and CO 2 reduced by 48%, 35%, 64% and 8%; the increase rates in the brake power and brake thermal efficiency are 17% and 11, respectively. The results indicated that SIM-TC-MC may be implemented into a diesel engine to control NO and to obtain higher engine performance. [ABSTRACT FROM AUTHOR]

A novelty of the Miller cycle with the asynchronous intake valve (AIVMC) was proposed and used in the test SI engine. In addition, the effects of the AIVMC on the combustion cycle-to-cycle variations and performance of the test SI engine were analyzed, and then compared to the experimental results of the Otto cycle (OC). The results indicated that the transient in-cylinder pressure distributions were discrete, and the peak combustion pressure distribution gradually dispersed with decreasing the intake valve spacing angle. The coefficient of variation of the indicated mean effective pressure (COV IMEP) of the test SI engine equipped with AIVMC were respectively 1.45% and 2.79% with using the spacing 90°CA and 50°CA under the low load, while the COV IMEP of the test SI engine equipped with AIVMC were respectively 0.79% and 3.45% with using the spacing 90°CA and 50°CA under the medium load. The application of AIVMC in the test SI engine effectively reduced the pumping mean effective pressure (PMEP) compared with OC. Under the operating condition of 2600 rpm and 8 bar, the EER of the test SI engine equipped with AIVMC (spacing 90°CA) was 13.0, which respectively increased 26.2% and 36.8% compared to the AIVMC (spacing 50°CA) and OC. • A novelty of Miller cycle with asynchronous intake valve (AIVMC) was proposed. • The PMEP of the SI engine with AIVMC greatly reduced compared with the OC. • The BSFC of the SI engine used the AIVMC (spacing 90°CA) was the lowest. • The application of AIVMC system in the SI engine effectively reduced COV IMEP. [ABSTRACT FROM AUTHOR]

• The research of asynchronous intake valve Miller cycle with 14.5 geometric compression ratio. • A comparative experimental investigation of Otto cycle and AIVMC was conducted. • Vortex flow is generated by asynchronous intake valve on the basis of tumble engine. • Compared with the baseline engine, the maximum improvement of BSFC is 7.7% with AIVMC. In this study, a series of comparative experiments were conducted on a gasoline direct ignition (GDI) turbocharged engine to investigate the effects of asynchronous intake valve Miller cycle (AIVMC) on the performance, combustion and emissions characteristics. The results show that using the asynchronous valve closing in the test engine can not only realize the Miller cycle, but also flexibly control the load, effectively reduce pump loss and improve fuel economy compared to the late intake valve closing. The minimum brake specific fuel consumption (BSFC) of the test engine equipped with and without the AIVMC are 235.59 g/kwh and 255.2 g/kwh at the condition of 2600 rpm and brake mean effective pressure (BMEP) 8 bar, which obtains a reduction of 7.7% compared to the baseline engine. In addition, the corresponding brake thermal efficiency (BTE) of test engine used the AIVMC is 35.6%, which is improved 8.2%. Besides, under the same geometric compression ratio, using the AIVMC in the test engine effectively improves the antiknock performance, keeps the 50% combustion location (CA50) closer to top dead center, shortens combustion duration, and expands the load range of low fuel consumption. As for emission performance, compared with baseline engine, though the application of AIVMC has lower mean in-cylinder temperature, the NOx emissions increases at low and medium loads but decreases at high load while HC emissions increases. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ( η Miller ) is higher than η Otto , when the multiplied result of the inlet pressure and Miller cycle coefficient ( δ M γ M ) 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 γ M 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 NO x 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study reports the influences of the engine design and operating parameters on the performance of a turbocharged, steam injected and Miller cycle diesel engine by using a simulation model based on the finite-time thermodynamics. The model is validated with experimental data and the effects of various engine design and operating parameters such as cycle temperature ratio, cycle pressure ratio, friction coefficient, engine speed, mean piston speed, stroke length, inlet temperature, inlet pressure, equivalence ratio, compression ratio, steam ratio, retarding angle and bore-stroke length ratio on the effective power and effective efficiency are investigated. Furthermore, the energy losses originating from incomplete combustion, friction, heat transfer and exhaust output are demonstrated by using figures. The results show that the engine performance increases with increasing some parameters such as cycle temperature ratio, cycle pressure ratio, inlet pressure; with decreasing some parameters such as friction coefficient, inlet temperature, steam ratio, retarding angle of intake valve closing. However, the engine performance could increase or decrease with respect to different conditions for some parameters such as engine speed, mean piston speed, stroke length, equivalence ratio and compression ratio. [ABSTRACT FROM AUTHOR]

The upcoming emission legislation for sea-going vessels issued by the international marine organization requires drastic reduction in nitric oxides. A well-known approach for meeting these requirements is to reduce the in-cylinder temperature prior to combustion by using the so-called Miller cycle. However, the mere use of this technique presents the actual limits due to long ignition delay, which occurs when the compression temperature is very low. As a consequence, premixed combustion develops quickly, increasing the local temperature in the combustion chamber and favoring NOx formation. Splitting the fuel injection into a small pilot and a main injection can reduce the magnitude of the premixed combustion and the local in-cylinder temperatures. The work presented here is divided in two parts and is novel by being the first systematic study of split injection combined with Miller cycle in large-bore engines. In its first stage, an extensive study of the injection dwell with two intake valve closings and three timings of the main injection are analyzed. In the second stage, both injection events are shifted later in the power stroke with fixed injection dwell. Overall, the pilot injection reduced the ignition delay but dropped the peak of the premixed combustion only with the most advanced intake valve closing. This improved fuel economy, but provided no advantages as far as emissions are concerned. In addition, while increasing injection dwell reduced NOx emissions, it also increased fuel consumption. The highest achieved NOx reduction was close to 60%, with a small drawback in fuel economy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Asynchronous LIVC Miller cycle can solve the problem of low combustion efficiency under low loads. • Asynchronous LIVC Miller cycle shortened combustion duration and lowered combustion cycle variation. • Asynchronous LIVC Miller cycle reduced the BSFC, especially at low and heavy loads. • One late intake valve closing can not only improve the knock resistance but also reduce the pump loss effectively. An experiment was conducted to explore the performance, combustion, and emission characteristics of the Miller cycle by asynchronous late intake valve closing (LIVC) on a direct-injection turbocharged gasoline engine. Asynchronous LIVC Miller cycle uses geometric compression ratio (GCR) of 12.5:1 (Miller-CR12.5), compared with Otto cycle original engine with GCR of 12.5:1 (Otto-CR12.5) and 10:1 (Otto-CR10). The study indicates that one late intake valve closing can not only realize the Miller cycle but also control the load to effectively reduce the pumping loss. When the brake mean effective pressure (BMEP) is below 4 bar, Miller-CR12.5 shows a very short combustion duration and lower combustion cycle variation compared with the Otto cycle, which solves the problem of low combustion efficiency due to the low actual compression ratio of the Miller cycle. In addition, the Miller cycle of asynchronous LIVC is similar to that of synchronous LIVC, which all can improve knock resistance at medium and high loads. Based on the above factors, Miller-CR12.5 reduces fuel consumption, especially at low and heavy loads. Besides, Miller-CR12.5 shows great fuel-saving potential at high speeds. In terms of emissions, Miller-CR12.5 significantly increases CO and THC emissions within the range of tested loads, but the NOx emissions are reduced under low and high loads. [ABSTRACT FROM AUTHOR]

The Miller cycle has been applied into the ICEs (internal combustion engines) to reduce NOx emissions, in the recent years. However, this method may decrease the engine power. The most common technique which improves the engine power is application of turbo charging. Thus, these two methods can be combined to make up for power loss and decrease emissions. In this study, the application of the Miller cycle and turbo charging methods into a single cylinder, four-stroke, DI (direct injection) diesel engine has been experimentally carried out. Two different versions of the Miller cycle, which provide 5 and 10 CA (crank angle) retarding compared to standard condition, are applied using two different camshafts. Turbo charging is applied at two different pressures, which are 1.1 and 1.2 bar, using a screw type compressor. In the results, the effective power and efficiency increased by 5.1% and 6.3%, NO, HC, CO and CO 2 decreased by 27%, 28%, 55% and 10%, respectively. The results show that combination of the proposed methods may be applied into the diesel engines to minimize NO and improve engine performance. [ABSTRACT FROM AUTHOR]

Emissions, especially NO x , released from diesel engines must be decreased to limit values described by the regulations because emissions have many bad effects on the environment. One of the known methods for reduction NO x emissions is to apply Miller Cycle to a diesel engine. In this study, Miller cycle is carried out by lowering the compression ratio according to the expansion ratio with closing the intake valve 30° crank angle later from the BDC (Bottom Dead Center) compared to standard diesel engine. Another method used is steam injection into diesel engine to decrease NO x emissions. And also, this method could be used to improve the performance and efficiency. Because of these positive effects, Miller cycle and steam injection methods could be implemented into diesel engines together. In this paper, Miller cycled diesel engine with steam injection has been modeled by using zero-dimensional two-zone combustion model. The obtained results have been compared with conventional diesel engine, Miller Cycled diesel engine and steam injected diesel engine in terms of performance and NO emissions. In the results, Miller Cycled diesel engine with steam injection is more efficient at low and medium engine speeds and has less NO emissions than conventional diesel engine, steam injected diesel engine and Miller Cycled diesel engine in all conditions. [ABSTRACT FROM AUTHOR]

Pollutant exhaust emissions, particularly NOx, produced by diesel engines must be reduced to limit values defined by the environmental regulations as the emissions have many harmful influences on the environment. Recently, the application of the Miller cycle into the internal combustion engines has been proposed to abate NOx emissions. In the present study, the Miller cycle with late intake valve closing (LIVC) version is applied into a single cylinder, four-stroke, direct injection, naturally aspirated diesel engine. Three different cam shafts have been manufactured to provide 5, 10 and 15 crank angle (CA) retarding compared to original camshaft. The optimum retarding angle has been determined as 5 CA in terms of NOx reduction. The attained results have been compared with conventional diesel engine which has standard CA (0 crank angle retarding) in point of the performance and NO, HC, CO emissions. In order to provide a model validation for engine torque, brake power, brake efficiency, specific fuel consumption (SFC) and NO, the Miller cycle diesel engine is modeled by using two-zone combustion model for 5 CA retarding at full load conditions. The simulation results have been verified with experimental data with non-considerable errors. In the experimental results, NO emissions decreased by 30% with 2.5% power loss and a remarkable change is not seen in the HC, CO emissions. The results show that the method could be easily applied into the diesel engine in order to minimize NO emissions. [ABSTRACT FROM AUTHOR]

The application of the Miller cycle into the internal combustion engines is proposed to decrease NOx emissions, in the recent years. Another NOx control technique is the steam injection method (SIM). In this study, the application of these methods together into a single cylinder, direct injection diesel engine is experimentally and theoretically performed. Two different Miller cycles, which provide 5 and 10 crank angle (CA) retarding compared to standard condition, are applied with two different camshafts. SIM is applied at three different injection rates which are 10%, 20% and 30% of the fuel mass. The results obtained are compared with standard conditions in terms of the performance and emissions. The simulation results are verified with experimental data with non-notable errors. In the experimental results, NO and CO 2 emissions decreased up to 48% and 2.2%; HC and CO emissions increased by 46% and 34% with the penalty by 6.4% and 9.2% for the effective power and efficiency. The optimum condition has been defined as 10 CA retarding and 30% steam injection rate (C62-S30) in terms of the maximum NO reduction. The results demonstrate that the combination can be applied into the diesel engines to minimize NO and CO 2 emissions. [ABSTRACT FROM AUTHOR]

Abstract: The future of compression ignition engines depends on their ability for keeping their competitiveness in terms of fuel consumption compared to spark-ignition engines. In this competitive framework, the Low Temperature Combustion (LTC) concept is a promising alternative to decrease NOx and soot emissions. Thus, this research focuses on implementing the LTC concept, but keeping the conventional mixing-controlled combustion process to overcome the well-known drawbacks of the highly-premixed combustion concepts, including load limitations and lack of combustion control. Two strategies for implementing the mixing-controlled LTC concept were evaluated. The first strategy relies on decreasing the intake oxygen concentration introducing high rates of cooled EGR (exhaust gas recirculation). The second strategy consists of decreasing the compression temperature by advancing the intake valves closing angle to reduce the effective compression ratio, compensating the air mass losses by increasing boost pressure (Miller cycle). These strategies were tested in a single-cylinder heavy-duty research engine. Additionally, 3D-CFD modeling was used to give insight into local in-cylinder conditions during the injection-combustion process. Results confirm the suitability of both strategies for reducing NOx and soot emissions, while their main drawback is the increment in fuel consumption. However, they present intrinsic differences in terms of local equivalence ratios and temperatures along combustion. [Copyright &y& Elsevier]

Abstract: The performance of an irreversible air standard Miller cycle in a four-stroke free-piston engine is analyzed using finite-time thermodynamic. In the model, the relation between the internal irreversibility described by using the compression and expansion efficiencies, the specific heat of the working substance depending on its temperature, the heat transfer loss as a percentage of fuel's energy and the friction loss computed according to the mean velocity of the piston is considered. Moreover, the influences of the excess air coefficient, initial temperature, compression ratio and another compression ratio corresponding to expansion level on the Miller cycle are analyzed by detailed numerical examples. The results show that the efficiency increases with the decrease of specific heat of working substance. The heat transfer loss and friction loss have negative effects on the performance. Comparison of the Miller and Otto cycles shows that the Miller cycle has a higher efficiency through extra expansion work. The conclusions of this investigation are of importance to provide guidelines for the performance evaluation and improvement of practical Miller engines. [Copyright &y& Elsevier]

Highlights: [•] At high load, LIVC is superior over EIVC in improving fuel economy. [•] The improvement with LIVC is due to advanced combustion phasing and increased pumping work. [•] At low load, EIVC is better than LIVC in improving fuel economy. [•] Pumping loss with EIVC is smaller than with LIVC at low load. [•] But heat release rate with EIVC is slower than with LIVC. [Copyright &y& Elsevier]

Highlights: [•] Paper explores the potential of the Miller cycle, applied to HSDI Diesel engines. [•] The benefit is the reduction of combustion temperature and NOx emissions. [•] The goal of the study is to assess the potential and the limits of this technique. [•] A 2.8L engine was selected, CFD tools have been calibrated through experiments. [•] CFD simulations shows a reduction of NOx and Soot of 25 and 60%. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a performance analysis based on the power output, thermal efficiency, maximum power output (MP) and maximum thermal efficiency (MEF) criteria have been carried out for an air-standard irreversible Dual–Miller cycle (DMC) with late inlet valve closing (LIVC) version which covers internal irreversibility owing to the irreversible-adiabatic processes. The thermal efficiency and power output are acquired based on the stroke ratio, cut-off ratio, pressure ratio, miller cycle ratio, cycle temperature ratio, cycle pressure ratio and the isentropic efficiencies of compression and expansion processes of the cycle. The influences of cycle temperature ratio and cycle pressure ratio of the DMC on the optimum performances are examined. [Copyright &y& Elsevier]

Abstract: This paper presents an investigation into the feasibility and potential advantages of a small scale Miller cycle natural gas engine for applications such as domestic combined heat and power systems. The Miller cycle engine is compared to a standard Otto cycle engine using cycle analyses and multidimensional simulation, and basic engine design implications are discussed. It is found that the Miller cycle engine has a potential for improved fuel efficiency, but at the cost of a reduced power to weight ratio. A fuel efficiency advantage of compared to a standard Otto cycle engine appears possible, however it is stated that further investigations, in particular into the topic of engine friction, are required in order to validate the findings. [Copyright &y& Elsevier]

• Multi-objective optimization model of key technologies in GDI engine was built. • The Pareto solution set was obtained by using MOGA-II genetic algorithm. • Knock Index was an important parameter which limited the engine performance improvement. Miller Cycle technology, High Compression Ratio technology and Variable Valve Timing (VVT) technology are the advanced technologies of the SI engine in hybrid vehicle at home and abroad. The best technical parameters under different operating conditions cannot be obtained easily through bench test due to the interaction among engine technologies. Therefore, this study picked up the above technologies on PSA 1.2THP engine simulation model, and the multi-objective optimization of the engine technologies scheme based on fuel economy was addressed. The optimization results which were selected based on fuel economy showed that with the increase of the geometric compression ratio, the knocking phenomenon was generated. However, the generation of knocking can be suppressed by adding the Miller Cycle technology, adjusting VVT and adjusting ignition timing. It was found that under the simultaneous action of Miller Cycle technology, High Compression Ratio technology and VVT, fuel economy and power can be balanced to achieve engine performance optimization. [ABSTRACT FROM AUTHOR]

Abstract: A conceptual analysis of the mechanism of the Miller cycle for reducing NO x emissions is presented. Two versions of selected Miller cycle (1 and 2) were designed and realized on a Rover “K” series 16-valve twin-camshaft petrol engine. The test results showed that the application of the Miller cycle could reduce the NO x emissions from the petrol engine. For Miller cycle 1, the least reduction rate of NO x emission was 8% with an engine-power-loss of 1% at the engine’s full-load, compared with that of standard Otto cycle. For Miller cycle 2, the least reduction rate of NO x emission was 46% with an engine-power-loss of 13% at the engine’s full-load, compared with that of standard Otto cycle. [Copyright &y& Elsevier]

Abstract: This study is aimed at examining the effects of heat loss characterized by a percentage of fuel''s energy, friction and variable specific heats of working fluid on the performance of an air-standard Miller cycle under the restriction of maximum cycle temperature. A more realistic and precise relationship between the fuel''s chemical energy and the heat leakage that is constituted on a pair of inequalities is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency where maximum power output occurs will increase with the increase of maximum cycle temperature. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the cycle increase while the efficiency decreases with the increase of specific heats of working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing friction loss. Comparison of the performance of air-standard Miller and Otto cycles are also discussed. Miller cycle has larger power output and efficiency than Otto cycle does, i.e., Miller cycle is more efficient than Otto cycle. It is noteworthy that the effects of heat loss characterized by a percentage of fuel''s energy, friction and variable specific heats of working fluid on the performance of a Miller-cycle engine are significant and should be considered in practice cycle analysis. The results obtained in the present study are of importance to provide a good guidance for the performance evaluation and improvement of practical Miller engines. [Copyright &y& Elsevier]

Abstract: In this paper, the performance of a Miller engine is evaluated under different specific heat models (i.e., constant, linear, and fourth order polynomial). Finite-time thermodynamics is used to derive the relations between power output and thermal efficiency at different compression and expansion ratios for an ideal naturally-aspirated (air-standard) Miller cycle. The effect of the temperature-dependent specific heat of the working fluid on the irreversible cycle performance is significant. It was found that an accurate model such as fourth order polynomial is essential for accurate prediction of cycle performance. The conclusions of this investigation are of importance when considering the designs of actual Miller engines. [Copyright &y& Elsevier]

Abstract: Using finite-time thermodynamics, the relations between thermal efficiency, compression and expansion ratios for an ideal naturally-aspirated (air-standard) Miller cycle have been derived. The effect of the temperature-dependent specific heat of the working fluid on the irreversible cycle performance is significant. The conclusions of this investigation are of importance when considering the designs of actual Miller-engines. [Copyright &y& Elsevier]

Abstract: The performance of an air standard Miller cycle with heat transfer loss and friction-like term loss was analyzed by using finite-time thermodynamics. The relation between the power output and the compression ratio, between the thermal efficiency and the compression ratio as well as the optimal relation between the power output and the efficiency of the cycle are derived. Moreover, the influences of heat transfer loss and friction loss on the cycle performance are analyzed by detailed numerical examples. The results obtained herein include the performance characteristics of different cycles in given conditions, which have universal guidance. [Copyright &y& Elsevier]

• Effect of engine technologies and mild hybridization on fuel economy was investigated. • Fuel consumption was reduced by more than 15% compared to the base vehicle. • The contribution of each technology to fuel consumption improvement were analyzed. 48 V mild hybrid electric vehicles (MHEVs) are considered to the prospective near-term solution for cost-effective vehicle electrification. In this study, the fuel consumption improvement of various synergistic engine technologies was experimentally investigated with a 48 V P0 mild hybridization. The details of application and optimization for each technology were considered and the effect of each technology was quantitatively identified. A combination of synergistic engine technologies including a high compression ratio, late intake valve closing strategy, high tumble flow, electric supercharging and exhaust gas recirculation was applied to a 1.4 L PFI engine. Engine test results confirmed that fuel consumption could be significantly improved by these technologies, and the maximum power and torque were increased as well. The vehicle test results showed that the application of synergistic engine technologies improved vehicle fuel economy by 10%. Engine optimization and EGR could enhance the fuel economy by 5.5% and the effect of electric supercharging and downspeeding resulted in a 4.5% fuel economy improvement. These improvements through the engine technologies were greater than the effect of 48 V mild hybridization which was verified to be 5.5% of the fuel economy enhancement. The result suggests that the application of synergistic engine technologies will be highly effective for improving fuel efficiency of MHEV. [ABSTRACT FROM AUTHOR]

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 COV IMEP. 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. [ABSTRACT FROM AUTHOR]

• The CVVL was used in the natural gas SI engine for replacing the throttle to control the load. • Economy and energy balance of the natural gas SI engine equipped a CVVL was qualitatively compared. • An extra 5.43% improvement of indicated thermal efficiency was obtained by using CVVL strategy. • Miller cycle was benefited to decrease the NOx emissions and mitigate knocking combustion. 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. [ABSTRACT FROM AUTHOR]

• The passive TJI system fueled by CNG is experimentally and numerically evaluated. • 1D numerical methodology helps to gain knowledge and improve the pre-chamber design. • Experimental results support the findings of the numerical methodology. • Increasing the pre-chamber volume has benefits under restrictive conditions. • An optimum swirl level inside the pre-chamber helps to stabilize combustion. 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. [ABSTRACT FROM AUTHOR]

Miller cycle and EGR have been proved to be the effective ways to improve the engine performance. In order to realize Miller cycle with high compression ratio, the piston and intake cam profile were redesigned for a turbocharged GDI engine. In-cylinder pressure was taken to clarify the difference of working cycles between Miller and Otto cycle. At full load, Miller engine with high compression ratio leads to the knock at a low speed. But at a high speed, engine can operate nearer stoichiometric conditions and get better economy. At partial load, engine can adopt higher compression ratio and intake pressure. The reduction of pumping losses and exhaust gas energy have become the key factors to improve fuel economy. On the basis, LP cooled EGR was introduced to study the further effect on Miller cycle. In-cylinder temperature is reduced due to the EGR dilution and heat capacity effect. Thus, engine can adopt larger ignition advance angle to obtain better combustion phase. For emission analysis, lower temperature can effectively reduce NO x emissions. However, because of the extended combustion duration and complex piston shape, insufficient combustion will result in the increase of THC. The constant excess-air coefficient makes the CO emissions almost unchanged. • The piston and intake cam profile are redesigned to realize high CR EIVC Miller cycle. • Theoretical indicator diagram reflects the advantages of Miller cycle over Otto cycle. • In low speed, Miller cycle can't eliminate the knock caused by high compression ratio. • Miller cycle with LP cooled EGR can obtain better fuel economy and lower NO X emissions. • The application of Miller cycle and EGR can further reduce exhaust losses. [ABSTRACT FROM AUTHOR]