Heat Release Analysis on Combustion and Parametric Study on Emissions of HCCI Engines Fueled with 2-Propanol-Heptane Blend Fuels

摘要

This article investigates the inhibition effects of a 2-propanol additive on n-heptane homogeneous charge compression ignition (HCCI) combustion, analyzes the relationship between the emissions with the combustion parameters and fuel component, and evaluates the influence of cold exhaust gas recirculation (EGR) on HCCI combustion and emissions. The experiments were conducted on a single-cylinder HCCI engine using neat n-heptane and 10～60% (by volume) 2-propanol-heptane blend fuels at 1800 rpm. The experimental results reveal that the ignition timing of the low-temperature reaction (LTR) is retarded, and the peak values of heat release during the LTR are decreased with an increase of 2-propanol in blend fuels. As a result, the ignition timing of the high-temperature reaction is delayed, both the maximum and lowest indicated mean efficient pressures (IMEP) are increased, and the combustion efficiency is also decreased. Parametric studies on CO and HC emissions show that the fuel volume with a high cetane number plays a major role in HC emissions. While the main parameter which has an important influence on CO emission is the maximum combustion temperature, other parameters including pressure rising rate, IMEP, and ignition timing have an indirect effect on CO emission. Moreover, the fuel component shows little effect on CO emissions. In the case of the operation stability of HCCI combustion, at a fixed fuel supplied energy for each cycle, the cycle-to-cycle variations of the maximum combustion pressure and its corresponding crank angle and ignition timing deteriorated with the an increase of the 2-propanol additive. Furthermore, EGR illustrates a substantial influence on the combustion and emissions of n-heptane for HCCI combustion doped with a high volume of the 2-propanol additive.