Miller Cycle Research Articles

Development of cycle-to-cycle variation of the tumble flow motion in a cylinder of a spark ignition internal combustion engine with Miller cycle

Reducing the cycle-to-cycle variation in an engine is a key to expanding the operational limits of high-efficiency engines such as lean-burn engines. The cycle-to-cycle variation of the engine output is caused by unstable combustion and is especially induced by the cycle-to-cycle variation of the in-cylinder flow. This investigation aims to clarify how the cycle-to-cycle variation of in-cylinder flow develops during intake and compression strokes. To achieve this aim, 12 kHz time-resolved particle image velocimetry measurements were conducted on the symmetrical vertical plane in a four-valve, four-stroke optically accessible engine. This study focuses on the relationship between the flow at the plug position at the ignition timing and the flow distribution in the intake and compression stroke. Correlation map analysis reveals this relationship, and some flow distributions are extracted. The fluctuations in the flow distribution induce the cycle-to-cycle variation of the flow direction at the plug position at the ignition timing, the position of the stagnation plane between the intake flow from the intake valves and the upper side of the tumble vortex, the strength of the blowback flow into the intake port generated by the Miller cycle, and the position of the tumble vortex in the late compression stroke. The flow distributions extracted by the correlation map analysis clearly change between cycles. These results also suggest that correlation map analysis is an effective way to elucidate the factors that induce the cycle-to-cycle variation of the in-cylinder flow.

Effect of the Intake Valve Lift and Closing Angle on Part Load Efficiency of a Spark Ignition Engine

This study provides an experimental evaluation of the effectiveness of Miller cycles with various combinations of lift and intake valve closing angle for a passenger car engine with premixed combustion in naturally aspirated operation. A fully variable electro-hydraulic valve train provided different valve lift profiles. Six load points, from 1.5 up to 5 bar brake mean effective pressure at a constant engine speed of 2000 min−1, were tested with 6 different intake valve lift/intake valve closing angle combinations. The intake valve closing angle was always set before bottom dead center to achieve the desired load with unthrottled operations. Experimental comparison with throttled operation outlines an indicated efficiency increase of up to 10% using high intake lift with early valve closing angle. Furthermore, this analysis outlines the influences that early intake valve closing angle has on fuel energy disposition. Longer combustion duration occurs using early intake valve closing angle because of turbulence dissipation effects, leading to slight reductions in the heat-to-work efficiency. However, overall pressure and temperature levels decrease and consequently heat losses and losses due to incomplete combustion decrease as well. Overall, we found that combustion deterioration is compensated/mitigated by the reduction of the heat losses so that reductions of pumping losses using early intake valve closing can be fully exploited to increase the engine’s efficiency.

Study of the Miller Cycle on a Turbocharged DI Gasoline Engine Regarding Fuel Economy Improvement at Part Load

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

Increasing the energy efficiency of the 6ChN13/15 duel-fuel engine using the Miller thermodynamic cycle

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.

Study on the Performance Factors of Two Stage Turbo-Charging System and Maximization of the Miller Cycle

Study on the Performance Factors of Two Stage Turbo-Charging System and Maximization of the Miller Cycle

EGR modeling and fuzzy evaluation of Low-Speed Two-Stroke marine diesel engines

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 EGR11HP EGR: high pressure EGR. and LP EGR22LP EGR: low pressure EGR.) 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 IMO33IMO: international maritime organization. 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.

Experimental and numerical investigations of charge motion and combustion in lean-burn natural gas engines

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.

Investigation of the Miller cycle on the performance and emission in a natural gas-diesel dual-fuel marine engine by using two zone combustion model

Compared to the standard cycle, the Miller cycle decreases the cylinder maximum combustion temperature which can effectively reduce NOX emissions. In this paper, a zero-dimensional two-zone combustion model is used to establish the simulation model of a marine dual-fuel engine, which is calibrated according to the test report under different loads. Due to the high emissions under part load, the Miller cycle (early intake valve closing method) is used for optimization. By analyzing the cylinder pressure, temperature, heat release rate and NOx emissions under different cases, it can be found that the effective working volume and thermal efficiency decrease with the advance of intake valve closing and improve with the increase of the geometric compression ratio. In all optimization cases, the NOX emissions and fuel consumption are reduced by 72% and 0.1%, respectively, by increasing the geometric compression ratio to 14 and the intake valve closing timing to 510 degree of crank angle (The reference top dead center is 360 degree of crank angle). The simulation results show that the early intake valve closing Miller cycle can effectively reduce the NOX emissions and cylinder peak pressure.

Driving Cycle and Elasticity Manoeuvres Simulation of a Small SUV Featuring an Electrically Boosted 1.0 L Gasoline Engine

<div class="section abstract"><div class="htmlview paragraph">In order to meet the CO<sub>2</sub> emission reduction targets, downsizing coupled with turbocharging has been proven as an effective way in reducing CO<sub>2</sub> emissions while maintaining and improving vehicle driveability. As the downsizing becomes widely exploited, the increased boost levels entail the exploration of dual stage boosting systems. In a context of increasing electrification, the usage of electrified boosting systems can be effective in the improvement of vehicle performances. The aim of this work is therefore to evaluate, through numerical simulation, the impact of different voltage (12 V or 48 V) electric superchargers (eSC) on an extremely downsized 1.0L engine on vehicle performance and fuel consumption over different transient manoeuvres. The virtual test rig employed for the analysis integrates a 1D CFD Fast Running Model (FRM) engine representative of a 1.0L state-of-the-art gasoline engine featuring an eSC in series with the main turbocharger, an electric network (12 V or 48 V), a six speed manual transmission and a vehicle representative of a B-SUV segment car. A preliminary assessment of the steady state performances of the 1.0L engine with the electrified dual boosting system with both 12 V and 48 V electric supercharger was performed. Then, the vehicle performances were evaluated by means of, on the one hand, vehicle elasticity manoeuvres for the performance assessment and, on the other hand, type approval and RDE driving cycles, for the fuel economy assessment. An evaluation of possible engine and vehicle hardware modifications was also carried out. In particular, the effect of a variation of the final drive ratio, the increase of the turbine size and the usage of a high efficiency engine concept (featuring an increased compression ratio from 10 to 12 and a late intake valve closing, exploiting the advantages of a Miller cycle) were investigated.</div></div>

Exploring the Potential of Miller Cycle with and without EGR for Maximum Efficiency and Minimum Exhaust Emissions in a Heavy-Duty Diesel Engine

Exploring the Potential of Miller Cycle with and without EGR for Maximum Efficiency and Minimum Exhaust Emissions in a Heavy-Duty Diesel Engine

Numerical Investigation of 48 V Electrification Potential in Terms of Fuel Economy and Vehicle Performance for a Lambda-1 Gasoline Passenger Car

Real Driving Emissions (RDE) regulations require the adoption of stoichiometric operation across the entire engine map for downsized turbocharged gasoline engines, which have been so far generally exploiting spark timing retard and mixture enrichment for knock mitigation. However, stoichiometric operation has a detrimental effect on engine and vehicle performances if no countermeasures are taken, such as alternative approaches for knock mitigation, as the exploitation of Miller cycle and/or powertrain electrification to improve vehicle acceleration performance. This research activity aims, therefore, to assess the potential of 48 V electrification and of the adoption of Miller cycle for a downsized and stoichiometric turbocharged gasoline engine. An integrated vehicle and powertrain model was developed for a reference passenger car, equipped with a EU5 gasoline turbocharged engine. Afterwards, two different 48 V electrified powertrain concepts, one featuring a Belt Starter Generator (BSG) mild-hybrid architecture, the other featuring, in addition to the BSG, a Miller cycle engine combined with an e-supercharger were developed and investigated. Vehicle performances were evaluated both in terms of elasticity maneuvers and of CO2 emissions for type approval and RDE driving cycles. Numerical simulations highlighted potential improvements up to 16% CO2 reduction on RDE driving cycle of a 48 V electrified vehicle featuring a high efficiency powertrain with respect to a EU5 engine and more than 10% of transient performance improvement.

Variable valve actuation–based combustion control strategies for efficiency improvement and emissions control in a heavy-duty diesel engine

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.

Improvement of engine performance with high compression ratio based on knock suppression using Miller cycle with boost pressure and split injection

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

Advanced Cylinder Deactivation with Miller Cycle

Advanced Cylinder Deactivation with Miller Cycle

A combination of electric supercharger and Miller Cycle in a gasoline engine to improve thermal efficiency without performance degradation

Miller cycle makes the expansion ratio larger than effective compression ratio by early or late closing intake valves thereby improving the thermal efficiency of gasoline engines at the risk of power degradation. Electric supercharging efficiently improves transient response and output of engines. This paper proposes an electrically supercharged non-backflow Miller cycle by combining electric supercharging and Miller cycle to improve thermal efficiency of gasoline engines without power output reduction. The results indicate that electrically supercharged non-backflow Miller cycle can effectively improve the thermal efficiency of gasoline engines. Compared to the original Otto-cycle gasoline engine, the electrically supercharged Miller-cycle engine has the highest thermal efficiency of 35.54% which is an improvement of 4.32% at 3500 rpm full load operation. The electric supercharger ensures that the power output is not reduced. Therefore, electrically supercharged non-backflow Miller cycle is an effective method to improve thermal efficiency of gasoline engines without performance degradation.

Numerical study on NOx and ISFC co-optimization for a low-speed two-stroke engine via Miller cycle, EGR, intake air humidification, and injection strategy implementation

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 combined with exhaust gas recirculation and post–fuel injection for emissions and exhaust gas temperature control of a heavy-duty diesel engine

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

The thermodynamic analysis of an electrically supercharged Miller Cycle gasoline engine with early intake valve closing

Electric superchargers are able to improve the thermodynamic process of gasoline engines by self-adapting running state to dominate intake air in all operation conditions. This paper proposes a novel approach for electrically supercharged Miller Cycle with early intake valve closing based on thermodynamics to settle the fuel economy problem of gasoline engines at low load operations by taking advantages of the domination of electric superchargers to intake air. Electrically supercharged Miller Cycle with early intake valve closing was realized by matching an electric supercharger, redesigning the inlet cam, and setting the intake valves closing before bottom dead center while keeping intake valves opening constant. An over-expanded engine cycle is attempted to be used to promote thermal efficiency by increasing geometric compression ratio, in addition to maintaining the effective compression ratio. Here, it has been attempted to systematically analyze the law of the energy losses of the electrically supercharged Miller Cycle gasoline engine with early intake valve closing using a reliable thermodynamic model from the perspective of heat engine. The results indicate that electrically supercharged Miller Cycle with early intake valve closing could improve the thermal efficiency of gasoline engines by significantly decreasing the pumping and exhaust losses.

Performance Analysis and Simulation of a Diesel-Miller Cycle (DiMC) Engine

A comprehensive performance examination of an engine running on combination of the Diesel and Miller cycles called Diesel-Miller cycle in terms of effective power, density of the effective power, and effective thermal efficiency, which will be called engine performance (ENPER) characteristics, is conducted using a novel thermodynamic simulation model. The impacts of cycle design parameters such as cycle pressure ratio, equivalence ratio, effective compression ratio (r), bore/stroke ratio (d / L), average piston speed, friction coefficient, engine speed (N), stroke (L), and air inlet temperature and air inlet pressure on the ENPER characteristics have been investigated. Additionally, the energy losses depending on exhaust output, friction, incomplete combustion, heat transfer have been defined as a ratio of energy provided by fuel injection. Variable specific heat values with respect to temperature variation for working fluid are used to get realistic results. The results of the study are reasonable and unique, and they could be utilized by researchers and engineers studying on internal combustion engines.

Computational study of NOx reduction on a marine diesel engine by application of different technologies

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.