• Energy Research

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.

A voltage degradation model for the low-pressure proton exchange membrane fuel cell (PEMFC) stack used in a fuel cell bus is presented: (1) the oxygen concentration term was derived from the PEMFC output voltage equation, and the concept of oxygen concentration resistance coefficient was introduced; (2) a 5 kW low-pressure PEMFC stack was used in this study. Two similar tests were carried out before and after the stack operating in the driving cycle for 640 h. First, the ohmic losses under different temperatures were measured using the current interrupt method and formulized with linear fitting method. Then, the oxygen concentration term was studied by the experiments with different air stoichiometric ratios while keeping the other operating parameters unchanged. The oxygen concentration resistance coefficient was obtained from the difference of voltages for the PEMFC stack in different air stoichiometric ratios using the genetic optimization algorithm. Then, the activation loss was obtained based on the PEMFC output voltage, the ohmic loss, and the concentration loss. The degradation model of the stack was built finally by comparing the two test results; (3) the correlation of the model to the actual experimental data is good; (4) the overvoltage of the stack with aging was analyzed using this model. The analysis showed that the activation overvoltage dominated the stack loss with about 80% of the total losses, followed by the ohmic loss. The concentration loss almost does not change with aging in the driving cycle condition; (5) the comparison of the simulation with the actual data from the PEMFC bus running for 30,000 km indicated that after 36,000 km the rated power of the PEMFC bus must be reduced.

Abstract Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature reactions are important for the partially premixed combustion. In the current study, a self-adaptive strategy is introduced to predict the motoring pressure by means of an equivalent isentropic index. The start of the low temperature reactions is detected when the pressure difference between the measured pressure and the predicted pressure is higher than a threshold value. Experimental results show that the maximum variation between the measured and the predicted motoring pressure before the top dead center is less than 0.02 bar. It is also demonstrated that the presented detection method is able to detect the start of the low temperature reactions under different engine operating conditions with varying injection timing, injection duration, number of injections and exhaust gas recirculation rate.

Abstract HCCI combustion can substantially reduce NOx and soot emissions of diesel engines. However it is hard for diesel HCCI to obtain the same level of fuel economy as traditional diesel engines. This paper presents a way to improve the fuel economy of diesel HCCI by adopting Integrated Starter Generator (ISG). A set of diesel parallel hybrid power system (in this article, we name it “hybrid engine”) is constructed by installing an ISG motor on a diesel engine, which applies HCCI–CI combined combustion. Based on a lot of investigation on diesel HCCI, this paper is focus on improving HCCI engine performance, especially the fuel economy, by adopting ISG motor assist control. The coordination control strategies of engine and ISG motor in HCCI transient states, HCCI–CI transition, engine quick start and braking energy regeneration are developed. The results of equivalent New European Driving Cycle (NEDC) tests show that, by using ISG assistance, the fuel consumption of the diesel HCCI engine is greatly reduced. Meanwhile the NOx and soot emission are also improved.

Abstract This paper investigates on cycle-to-cycle variation of dieseline fueled PPCI engine and introduces a closed-loop control method based on in-cylinder pressure sensor. Experiments are performed on a four-cylinder compression ignition engine. Results show that p max (maximum in-cylinder pressure) and θ pmax (crank angle where p max occurs) cannot be properly identified by the control system. Thus, COV (coefficient of variation) of p max and θ pmax cannot reflect the real combustion fluctuation level. IMEP (indicated mean effective pressure) contains information about the whole combustion process for it is calculated by all the sampled pressure of the current cycle. Therefore, COV imep can be chosen as the combustion stability indicator to evaluate cycle-to cycle variation. Besides, sweep experiments of injection timing (IT) and exhaust gas recirculation (EGR) are conducted to investigate the influence of these control parameters on COV imep and MPRR (maximum pressure rise rate). COV imep is the indicator of combustion stability while MPRR is related to the noise level. Based on detailed analysis of experimental results, a model-based combustion stability closed-loop control algorithm is proposed in order to ensure good combustion stability on the premise that the noise of engine can also be limited (which means COV imep and MPRR can be restrained below their threshold) by an acceptable level. The simulation results show that COV imep and MPRR can be restrained simultaneously under different loads.

In this paper, a kind of on-board liquid hydrogen (LH2) cold energy utilization system for a heavy-duty fuel cell hybrid truck is proposed. Through this system, the cold energy of LH2 is used for cooling the inlet air of a compressor and the coolant of the accessories cooling system, sequentially, to reduce the parasitic power, including the air compressor, water pump, and radiator fan power. To estimate the cold energy utilization ratio and parasitic power saving capabilities of this system, a model based on AMESim software was established and simulated under different ambient temperatures and fuel cell stack loads. The simulation results show that cold energy utilization ratio can keep at a high level except under extremely low ambient temperature and light load. Compared to the original LH2 system without cold energy utilization, the total parasitic power consumption can be saved by up to 15% (namely 1.8 kW).

Abstract Power split configurations exhibit potential on decreasing fuel consumption. However, how to select the best power split configuration among all the possible configurations still need to be explored. In this paper, a one-dimensional searching ECMS (Equivalent Consumption Minimization Strategy) is developed to evaluate fuel consumption for input power split configuration. Additionally, a battery degradation model based on experimental data is applied to evaluate the battery degradation for input power split configuration. According to one-dimensional searching ECMS and battery degradation model, the impact of different input power split configurations on fuel consumption and battery degradation is investigated. Simulations show that configuration T1 has fuel consumption and battery degradation advantages for PHEV city bus application in China. These advantages are observed because the system efficiency operation points of configuration T1 are closer to the high efficiency area than the system efficiency operation points of other input power split configurations. Furthermore, according to the lever model and one-dimensional searching ECMS method, a power split configuration selection method is provided in this paper. The simulation results based on configuration selection method still indicate that configuration T1 appears to have the best fuel economy for PHEV city bus application. Moreover, configuration T5, with a lever length close to 0, exhibits the worst fuel consumption and battery degradation.