Comparison of the transient response of a compression ignition engine running with gasoline, naphtha, and methanol as fuels

Abstract

This study conducted a detailed investigation to evaluate the transient operation of a compression ignition engine using three low-reactivity fuels. The fuels tested were gasoline, methanol, and naphtha. This research gives valuable insight into how these alternative fuels behave under dynamic operating conditions compared to stationary conditions. Employing a comprehensive two-part methodology, the study firstly undertakes experimental procedures involving parametric sweeps to optimize the engine performance across three operating conditions, and a dedicated calibration was achieved for the engine operation for each of the three fuels. With this calibration, two transient cycles were proposed for evaluating the engine response regarding the injection system, air management system, and emissions. The transient response was assessed through load variations at fixed engine speeds and combined cycles of speed and load transitions. The second part of the work covered a numerical assessment using GT-Power to simulate global emissions in a Class 3 WLTC. The findings reveal that naphtha outperforms other LRFs like methanol and gasoline in torque response and stability in fixed-speed cycles. Methanol, while exhibiting almost negligible soot emissions, encountered significant combustion stability challenges under low-load conditions, rendering it less suitable for exclusive use in real vehicle scenarios. On the other hand, naphtha showed promising results as a diesel alternative in the WLTP cycle, achieving similar torque and speeds, with a substantial reduction of 40 % in NOx emissions, a slight increase of 9 % in soot emissions, and an important reduction of 10 g CO2/km in carbon impact. However, the rise in unburned hydrocarbon species poses a challenge for meeting tailpipe emissions regulations.