Fuel Composition Effects on Combustion Characteristics of a Low-Temperature Gasoline Combustion Engine

<div class="section abstract"><div class="htmlview paragraph">Low Temperature Gasoline Combustion (LTGC) in compression ignition engines is controlled by chemical kinetics and the autoignition reactivity of the fuel-air mixture, which are heavily influenced by the composition of the fuel. To investigate fuel-engine interactions, experiments were performed on a single-cylinder LTGC engine at various operating conditions with three premium-grade gasoline-like fuels with nominally the same octane rating but with high aromatic (HA), high cycloalkane (HCA) and high ethanol (E30 - 30%<sub>vol</sub>) contents, respectively. At fully-premixed naturally aspirated conditions, E30 showed the highest autoignition reactivity followed by HCA and HA. However, reactivity differences became less relevant when direct-injecting the fuel because of the vaporization cooling effect on the in-cylinder reactivity, which compensated for differences in fuel’s chemistry. Intake pressure sweeps demonstrated that the autoignition reactivity of E30 had the highest sensitivity to pressure, whereas HCA was the least sensitive likely due to the radical-scavenging activity of cyclo-pentane, a major component of HCA. Exhaust gas recirculation (EGR) addition was required to maintain stable engine operation at high intake pressures, with E30 requiring the highest EGR rate followed by HA and HCA. Only HA showed low temperature heat release at high intake pressures, and HA was also found to have the highest φ-sensitivity among all the fuels likely because of the stronger low temperature chemistry of this fuel. A combination of these two factors aided in extending stable engine operating limits for HA by maintaining engine stability at retarded combustion phasing. Interestingly, the optimum fuel composition changes depending on the engine operating conditions, with high ethanol content being desired at naturally aspirated conditions due to the lower intake heating requirement, high cyclo-alkane content being desired at high pressures due to the lower EGR requirement, and high aromatic content being desired at high loads due to the higher combustion stability and φ-sensitivity.</div></div>