Ozone Seeding Effect on the Ignition Event in HCCI Combustion of Gasoline-Ethanol Blends 2017-01-0727
The transportation sector adds to the greenhouse gas emissions worldwide. One way to decrease this impact from transportation is by using renewable fuels. Ethanol is a readily available blend component which can be produced from bio blendstock, currently used blended with gasoline from low to high concentrations. This study focuses on a high octane (RON=97) gasoline blended with 0, 20, and 50, volume % of ethanol, respectively. The high ethanol blended gasoline was used in a light duty engine originally designed for diesel combustion. Due to the high octane rating and high ignition resistance of the fuel it required high intake temperatures of 443 K and higher to achieve stable combustion in in homogeneously charged compression ignition (HCCI) combustion operation at low load. To enable combustion with lower intake temperatures more commonly used in commercial vehicles, ozone was injected with the intake air as an ignition improver. Experiments showed that the intake temperature could be significantly reduced and with ozone seeding at an engine speed of 1500 rpm and an equivalence ratio of 0.3 stable combustion was shown at an intake temperature of 413 K for all fuel blends. According to earlier studies, the ozone decomposes into oxygen radicals, which assists in the pre-reactions and therefore enable the use of lower intake temperatures than without the use of ozone. The purpose of this study was to chart the ignition improver effect of ozone HCCI combustion on gasoline fuels with various concentrations of ethanol by looking at the autoignition and combustion initiation temperatures, defined as CA2 (2% of the total fuel burnt) and a combustion rate of 0.3 J/CAD, respectively. It was shown that stable combustion could be enabled for intake temperatures that without ozone led to misfire, and ozone was seen to promote pre-reactions. Larger amounts of ozone were required at increased ethanol concentrations.