Combustion and emission characteristics of Multiple Premixed Compression Ignition (MPCI) mode fuelled with different low octane gasolines

This paper studies the combustion and emission characteristics of three low octane fuels: naphtha, the blend of gasoline and diesel (G70D30), and the blend of gasoline and n-heptane (G70H30) in Multiple Premixed Compression Ignition (MPCI) mode. A commercial diesel fuel is also tested in conventional diesel combustion mode and double injection mode as a comparison. The study is carried out in a single cylinder diesel engine with a compression ratio of 16.7. By varying the common rail pressure, the effect of injection pressure on combustion and emissions is investigated. The results illustrate that the combustion delay of the gasoline-type fuels is extended with the increase of injection pressure. The soot emission decreases at high injection pressure with a penalty of higher CO and HC emissions. Increasing the injection pressure also reduces the particle number in accumulation mode, but produces more in nucleation mode. Among the test fuels, naphtha has the lowest NO emission due to low combustion temperature but the highest CO and HC emissions. There is no significant difference in particle size distribution for the three fuels. The indicated thermal efficiency of gasoline-type fuels increases with the rise of injection pressure and is higher than that of diesel at high injection pressure. Naphtha has the highest efficiency as a result of its low heat transfer and exhaust loss. The diesel fuel has lower CO and HC emissions than the gasoline-type fuels do, but much higher pressure rise rate, NO and soot emissions due to high combustion temperature and poor premixing. Therefore, the low octane gasoline fuels are more suitable than the diesel for compression ignition engines in terms of the emissions. (C) 2015 Elsevier Ltd. All rights reserved.