Development of an empirical test method to quantify the ɸ-sensitivity of liquid fuels

Abstract

Several researchers are investigating strategies to lower the emissions and increase the efficiency of combustion engines to reduce the negative impact on the environment and the climate from transportation. The low-temperature combustion (LTC) concept is the basis for some of these high-efficiency, low-emission combustion technologies. To maximize the combustion controllability of engines based on the LTC concept, the combustion behavior of fuel both at different equivalence ratios (ɸ) and under ɸ sweeps must be understood and planned precisely. The ɸ-sensitivity of a fuel explains its behavior at different engine loads or stratification levels. In this study, a new test method for empirically evaluating ɸ-sensitivity using a Cooperative Fuel Research (CFR) engine is proposed and the validity of the method is investigated. A modified CFR engine for homogeneous-charge compression ignition (HCCI) combustion is used to investigate the compression ratio (CR) sensitivity of different toluene–ethanol reference fuels (TERFs) in a research octane number (RON) range of 63–105. This study suggests a method to quantify the ɸ-sensitivity of different fuels and blends by measuring the compression ratio required to keep the CA50 constant while varying ɸ. It shows that the fuel composition greatly affects the fuel ɸ-sensitivity even for different blends with the same RON. The results also indicate that the coexistence of ethanol and toluene in a blend can generate the highest ɸ-sensitivity of the blend compared to other blends with the same RON. Fuel composition has a strong effect on emissions. The simultaneous effect of fuel composition and ɸ variation on the emission and stability parameters is nonlinear.