Particulate Matter (PM) emissions from gasoline direct injection (GDI) engines, particularly Particle Number (PN) emissions, have been studied intensively in both academia and industry because of the adverse effects of ultrafine PM emissions on human health and other environmental concerns. GDI engines are known to emit a higher number of PN emissions (on an engine-out basis) than Port Fuel Injection (PFI) engines, due to the reduced mixture homogeneity in GDI engines. Euro 6 emission standards have been introduced in Europe (and similarly in China) to limit PN emissions from GDI engines. This article summarises the current state of research in GDI PN emissions (engine-out) including a discussion of PN formation, and the characteristics of PN emissions from GDI engines. The effect of key GDI engine operating parameters is analysed, including air-fuel ratio, ignition and injection timing, injection pressure, and EGR; in addition the effect of fuel composition on particulate emissions is explored, including the effect of oxygenate components such as ethanol.

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The resurgence of aviation heavy fuel engines (HFEs) and the single fuel concept policy make it important to investigate the application of kerosene in aviation compression ignition engines. From the experience of automotive engines, biofuels, in particular higher alcohols, may offer better combustion and emission characteristics for HFEs. In this study, the combustion performance was analyzed in a commercial aircraft compression ignition engine burning diesel as a baseline fuel and Chinese aviation kerosene fuel (RP-3) blended with pentanol (so-called second generation biofuel) with different blending ratios. The injection timing as the most critical operational parameter was swept from 17 to 23°CA BTDC (crank angle before top dead center) under constant engine speed (1600 rpm) and fixed injection pressure (60 MPa). The indicated thermal efficiency of kerosene−pentanol blend (K60P40) was higher than those of all other test fuels, and the advancement in injection timing caused an increase in combustion temperature which improved both the indicated thermal efficiency and combustion efficiency. The combustion duration was shorter for kerosene−pentanol blends (K60P40 and K80P20) than diesel; however, the combustion duration considerably increased with advancing injection timings for all the test fuels. Kerosene and its pentanol blends showed longer ignition delay compared to baseline diesel due to their lower cetane numbers. The indicated specific fuel consumption (ISFC) values of K80P20 and K60P40 were demonstrated to be lower than that of baseline diesel. This work demonstrated the great potential of kerosene−pentanol fuel blends in aircraft diesel engines without significant modifications.

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Dimethyl ether (DME) and n-pentanol can be derived from non-food based biomass feedstock without unsettling food supplies and thus attract increasing attention as promising alternative fuels, yet some of their unique fuel properties different from diesel may significantly affect engine operation and thus limit their direct usage in diesel engines. In this study, the influence of n-pentanol, DME and diesel blends on the combustion performance and emission characteristics of a diesel engine under lowtemperature combustion (LTC) mode was evaluated at various engine loads (0.2-0.8 MPa BMEP) and two Exhaust Gas Recirculation (EGR) levels (15% and 30%). Three test blends were prepared by adding different proportions of DME and n-pentanol in baseline diesel and termed as D85DM15, D65P35, and D60DM20P20 respectively. The results showed that particulate matter (PM) mass and size-resolved PM number concentration were lower for D85DM15 and D65P35 and the least for D60DM20P20 compared ACCEPTED MANUSCRIPT with neat diesel. D60DM20P20 turned out to generate the lowest NO x emissions among the test blends at high engine load, and it further reduced by approximately 56% and 32% at low and medium loads respectively. It was found that the combination of medium EGR (15%) level and D60DM20P20 blend could generate the lowest NO x and PM emissions among the tested oxygenated blends with a slight decrease in engine performance. THC and CO emissions were higher for oxygenated blends than baseline diesel and the addition of EGR further exacerbated these gaseous emissions. This study demonstrated a great potential of n-pentanol, DME and diesel (D60DM20P20) blend in compression ignition engines with optimum combustion and emission characteristics under low temperature combustion mode, yet long term durability and commercial viability have not been considered.