Effect of ethanol blending on particulate formation from premixed combustion in spark-ignition engines

Particulate formation due to combustion of a wide range of ethanol-gasoline blends were investigated in an internal combustion engine. The engine used for this study is a single-cylinder research engine, the architecture of which is representative of a modern spark ignited direct injected (SIDI) engine. Instead of direct injection, the engine was fueled using a premixed prevaporized (PMPV) mode, which supplied the fuel to the engine in a well-mixed, gas-phase air-fuel mixture in order to isolate physical effects of the fuel. This created a completely homogenous air-fuel mixture with no pockets of significantly differing equivalence ratio, liquid fuel droplets, or wetted surfaces, ensuring that particulate formation was due to homogenous, gas-phase combustion. The engine was operated at a fixed load and phasing so that the effects of varying equivalence ratio and ethanol content could be examined. The results in this work show that the addition of ethanol results in a consistent decrease in engine-out particulate proportional to ethanol content. Moreover, the critical equivalence ratio, the equivalence ratio at which significant sooting begins, increases in a linear fashion with ethanol addition. It was also shown that the shape of the particulate size distribution (PSD) is affected by ethanol content, with increased ethanol leading to more nucleation-mode dominated distributions.