• Energy Research
• 2016-2025close

Abstract The start of combustion (SOC) has a direct impact on the intensity of heat release and an indirect effect on engine noise and pollutant formation. Because ignition delay can vary during the system’s lifetime due to changes in fuel quality or gradual deterioration of the engine and injection system, real-time detection of the SOC is required to optimize engine performance. In this study, engine compression and expansion strokes are treated as polytropic processes based on a thermodynamic analysis of cylinder pressure signals where the polytropic exponent is defined as an equivalent isentropic index. A real-time SOC detection method applying the first derivative of the equivalent isentropic index is proposed. The presented method using two-stage threshold levels of 0.4 and 0.1 is free of exponential and logarithmic computations, significantly reducing calculation time. It is implemented in a real engine control unit (ECU) and validated in both stationary and transient conditions. Test results show that this method is able to detect multiple SOCs caused by multiple injections and has latencies of 0.5 °CA, 0 °CA and 0 °CA to the separation points of cylinder pressure from motoring pressure at three engine operation points.

Abstract This paper presents a study on the upper load expansion and combustion characteristics of a multi-mode combustion engine with dieseline. The partially premixed compression ignition (PPCI) mode with early direct injection and late-injection low temperature combustion (L-LTC) mode with near-top dead center (TDC) direct injection are studied and compared at various loads with sweeps of injection parameters and exhaust gas recirculation (EGR) rates. A single injection strategy and a double injection strategy with small pilot ratios are tested. For both combustion modes, the criteria are set to identify the load limit of clean combustion. The NOx limit is 200 ppm, and the particulate matter number limit is 100 × 106/cm3. The maximum pressure rise rate is lower than 0.8 MPa/°, and the maximum cylinder pressure is below 16 MPa. In addition, the coefficient of variation for the indicated mean effective pressure (IMEP) should be less than 3% combustion stability. The results indicate that L-LTC has a higher load limit than PPCI for all the test fuels; therefore, the upper load limit of PPCI can be increased using L-LTC. However, the thermal efficiency of L-LTC is lower than that of PPCI. Therefore, a multi-mode combustion strategy is proposed to be the best option for the whole load range. For the small to medium load range, PPCI can achieve a low emissions level and with a higher thermal efficiency than L-LTC; therefore, PPCI is an ideal choice for this range. For the medium to high load range, the L-LTC mode is the only suitable mode due to its low emissions. In the high load range, a simultaneous reduction in NOx and PM is not possible for both PPCI and L-LTC; therefore, the conventional CI mode has to be used to ensure high fuel economy performance.

Abstract PHEVs have shown their potential to further reduce fuel consumption and emissions, and many OEMs have put forward their mass-produced PHEV models. However, the series-parallel configuration PHEVs are seldom seen in the market. This paper discusses the testing and analysis of a Honda Accord PHEV, whose powertrain configuration is series-parallel. The NEDC cycle test, dynamic acceleration test, and static cruise test are finished in a four-wheel drive chassis dynamometer at the China Automotive Engineering Research Institute. Powertrain configuration design, control strategy, and fuel economy of the vehicle are analyzed. The test results show that the series-parallel configuration has the potential to reduce transmission mechanical losses, and the series operating mode tends to be more efficient in most working conditions.

Abstract Partial premixed compression ignition (PPCI) combustion is one of the most promising concepts to achieve combustion with high efficiency and low engine emissions. Glow plugs can be utilized to increase the combustion stability of PPCI combustion at idle or low loads, assisting the auto-ignition of gasoline or fuel with high octane number, which are major challenges remaining in PPCI combustion. The low load ignition assist application of glow plug is quite different from the traditional cold start assist. Other than simply heating the air in the cylinder, in the PPCI application the glow plug needs to heat the charge to specific temperatures at specific time, because the heating is vital to the ignition timing control in PPCI combustion. As a preliminary work of PPCI combustion low load assist application, in this paper infrared thermometer and some other devices were utilized to study the performance of representative glow plugs in open air. Based on the experiments, GPCU (glow plug control unit) was designed, open-loop and closed-loop temperature control algorithms were proposed. Further a lumped heat capacitance model of the glow plug was built based on system identification to study glow plug surface temperature behavior. It was found that PSG glow plug has excellent performance, maximum temperature of more than 1200°C was observed, 600 °C surface temperature was achieved in around 3 seconds. Open-loop temperature control was verified on GPCU; two glow plug temperature models were proposed, which can estimate the glow plug temperature for feedback control.