Investigation of RCCI Characteristics of Combustion and Emissions With PFI of N-Butanol and Direct Injection of High Linoleic Content Biodiesel

Abstract

This study investigated the RCCI (Reactivity Controlled Compression Ignition) of PFI (Port Fuel Injection) of n-butanol with direct injection (DI) of a high linoleic acid content biodiesel, cottonseed (CS100). The experimental omnivorous-fuel engine was operated at 1400 rpm and 6 bar indicated mean effective pressure (IMEP) with 20% cooled EGR. The mass ratio of n-butanol injected comprised of 50% of the total fuel mass. The dual fueling strategy of RCCI changed the conventional diesel combustion (CDC) apparent heat release profile. With the new fueling strategy the heat release was split into two regions of high temperature heat release when using CS100. The first occurred before top dead center (BTDC) from the high reactivity fuel and the second peak occurred due to the combustion of the low reactivity fuel (n-butanol) after top dead center (ATDC). ULSD did not produce this same split in heat release due to the longer ignition delay. The ignition delay for CS100 was shortened by 0.15 ms when compared to ULSD because of the high palmitic acid content in the biodiesel. The RCCI process itself extended the ignition delay about 0.17 ms (about 1.4 CAD) suggesting the possibility of controlling combustion phasing for both RCCI fueling strategies of ULSD and CS100. The CA50 occurred similarly at 10° ATDC for ULSD and CS100 however, RCCI shifted the CA50’s (7° and 8° ATDC for CS100 and ULSD respectively). Soot emissions exhibited a decrease with the PFI of n-butanol because of the highly oxygenated nature of the fuel by 80%. In summary, RCCI stratification using n-Butanol as the low reactivity fuel significantly reduced soot emissions when using either a high linoleic acid content biofuel or ULSD while also suggesting control over combustion phasing.