Research on and development of a Miller cycle engine with multi-stage boosting

Proceedings of the Institution of Mechanical Engineers, Part D:

2016

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

Section: Experimental Set-upmentioning

confidence: 68%

Development of a Miller cycle engine with single-stage boosting and cooled external exhaust gas recirculation

Proceedings of the Institution of Mechanical Engineers, Part D:

2016

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“…The geometric compression ratio (CR) of the Miller cycle engine was increased to 12.0:1 by redesigning the piston crown geometry. 22 To achieve a high geometric CR of 12.0:1, the effective CR has to be reduced in order to avoid abnormal combustion including excessive knock and pre-ignition at higher engine loads. A LIVC cam strategy was implemented using a longer-duration intake cam to delay significantly the intake valve closing, which was demonstrated to reduce the effective compression ratio for knock suppression excellently and to allow significant advance in the combustion phasing.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…The developed model of the Miller cycle engine (with a high CR of 12.0:1, the 40° CA longer-duration LIVC cam and the TC–SC boosting system) was validated first using the steady-state engine measurement data obtained in an earlier study, 22 which used the V400 supercharger in the TC–SC boosting system.…”

Section: Model Descriptionmentioning

confidence: 99%

“…A 2.0 l Miller cycle SI engine with two-stage boosting and variable valve actuation was developed in previous work. 22 The experimental results demonstrated that a high expansion ratio of 12.0:1 was achievable on the downsized boosted SI engine to reduce the fuel consumption by 3–4% using the late-intake-valve-closing (LIVC) cam with an opening duration 40° crank angle (CA) longer than the baseline to reduce the effective compression ratio and to control knock; the two-stage boosting system enabled the Miller cycle engine to maintain the same torque and power performance as the baseline single-stage turbocharged engine by providing higher boost ratios to make up the reduced trapped mass and the engine torque due to the LIVC. The two-stage turbocharger (with two turbochargers of different sizes arranged in series) was the preferred choice for the two-stage boosting system rather than the TC–SC combination with a V400 supercharger.…”

Section: Introductionmentioning

confidence: 99%

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Optimization of a turbocharger and supercharger compound boosting system for a Miller cycle engine

Proceedings of the Institution of Mechanical Engineers, Part D:

2017

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

“…Miller cycle engines use Late-Intake-Valve-Closing (LIVC) or Early-Intake-Valve-Closing (EIVC) to reduce effective compression in order to enable a higher geometric compression ratio (CR) or expansion ratio (ER), which has shown to effectively improve engine thermal efficiency while controlling knock and abnormal combustions on downsized boosted spark-ignition (SI) engines. 2–12…”

Section: Introductionmentioning

confidence: 99%

Development of an aggressive Miller Cycle engine with extended Late-Intake-Valve-Closing and a two-stage turbocharger

Proceedings of the Institution of Mechanical Engineers, Part D:

2017

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