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Particulate matter (PM) emitted from conventional diesel engines has significant deteriorating effects on natural environment and human health. Among alternative oxygenated fuels, polyoxymethylene dimethyl ether (PODE) is a novel renewable fuel with high cetane number, oxygen content and volatility, and has prominent potential for reducing the PM emissions. In this study, the influences of fuel injection parameters, including injection pressure and injection timing on the reduction of PM emissions were explored for a four-cylinder diesel engine fueled with PODE/diesel blends at various engine loads. The three blends were the pure diesel (denoted as P0), a mixture of 80% diesel and 20% PODE (denoted as PD20), and the mixture of 70% diesel and 30% PODE (denoted as PD30). The results showed that adding PODE to diesel resulted in a reduction in both the total particle number concentration (PNC) and the particle mass concentration (PMC) at all loads. For the PODE/diesel blends, at low load and higher injection pressures, the PMC further decreased, although the value of PNC drastically increased. For the PODE/diesel blends, at medium load and higher injection pressures, both the PNC and PMC values decreased. When the injection pressure was higher than 120 MPa, it could not continuously reduce PNC. Furthermore, for the PODE/diesel blends, at high load and high injection pressures, both the PNC and PMC values greatly decreased. The PODE/diesel blends coupled with the retarded injection timing could reduce the PNC and PMC values, but when the injection timing occurred too close to the top dead center (TDC), the PNC value increased. In addition, as the injection timing was closer to TDC, the effect of the addition of PODE in diesel fuel on reducing PNC and PMC became more significant.

Effects of increasing compression ratio (CR) and intake boosting when operating engine with cooled EGR are characterized and compared in a single cylinder, port-fuel injection SI engine. CR and intake pressure is independently increased form 8:1 to 10:1, and 1.0 to 1.4 bar when operating EGR from 0% to 20%. Experiments are performed at constant speed 1200 r/min, full load and stoichiometric air fuel ratio. As increase of EGR, the MBT (minimum ignition advance for best torque) spark timing has to be advanced to compensate retarded combustion phasing caused by the cooling effect of EGR. Increasing intake pressure to 1.4 bar gains more restore in maximum cylinder pressure and peak heat release rate compared with those by increasing CR to 10:1. At full load, increase of EGR produces a significant drop in IMEP. Increasing intake pressure and CR can both effectively restore egnine IMEP while achieving a reduction in ISFC (indicated specific fuel consumption) and COVIMEP (coefficient of cyclic variation of IMEP). Increase of CR and intake pressure also alleviates the deterioration in HC emissions, where the decrease of HC is up to 34% at 20% EGR. However, slightly higher NOX is produced at higher CR and intake pressure.

To reduce the cyclic variation is an effective way to improve the fuel economy and combustion of spark ignition engines. In this paper, the effect of exhaust gas recirculation (EGR), compression ratio and boost pressure on cyclic variation was investigated by means of both experiments and simulation for a port fuel injection (PFI) engine. The mechanisms of these effects were analyzed by computational fluid dynamics (CFD) tools. A Ricardo E6 PFI engine was used as the experimental prototype. The experiments were performed with six EGR ratios, three compression ratios and two boost pressures for a given equivalence ratios. The experiments were operated with the same parameters as that of the simulation. Results showed that the simulation work agree well with the experiment. Both simulation and experiment results showed that an increase of EGR ratio will increase cyclic variation for its lower laminar flame speed. However, the combination of EGR with either an appropriate compression ratio or boost pressure can achieve a relatively low cyclic variation.

Fuel and engine interactions are the essential issues for advanced compression ignition engines, and low-octane gasoline is considered as prospective fuel under compression ignition conditions. However, with enhanced low-temperature chemistry, low-octane gasoline may exhibit distinctive characteristics affecting ignition phenomena. In this study, the ignition phenomena of low-octane gasoline was investigated under gasoline compression ignition conditions using validated chemical kinetic mechanism. The toluene primary reference fuel blends were employed to obtain the same RON = 75 with various octane sensitivity. With addressing ignition characteristics and pre-ignition heat release, the role of fuel sensitivity, inlet conditions, and exhaust gas recirculation on fuel reactivity was clearly demonstrated. The results show that the fuel sensitivity is positively correlated with fuel reactivity in high-temperature low-pressure regime, whereas there is a negative correlation in low-temperature high-pressure regime. The opposite correlation between fuel sensitivity and fuel reactivity is closely related to the pre-ignition heat release, with decreasing low-temperature heat release at high fuel sensitivity. Finally, the effects of exhaust gas recirculation on low-temperature heat release were investigated. It shows that affected by low-temperature heat release, distinct characteristics in combustion phasing are observed with the addition of the exhaust gas recirculation.