Effects of Fuel Injection Timing on Combustion and Emissions of a Spark-Ignition Methanol and Methanol/Liquefied Petroleum Gas (LPG) Engine during Cold Start

The combustion and emission characteristics of spark-ignition (SI) methanol and methanol/liquefied petroleum gas (LPG) engines under different fuel injection timings during cold start have been studied by means of a cycle-by-cycle control strategy. The results showed that the methanol injection timing, the LPG injection timing, and the LPG injection timing delay relative to the methanol injection timing affect cold-start combustion characteristics and emissions of hydrocarbons, formaldehyde. and unburned methanol significantly. The methanol injection timing, the LPG injection timing, and the LPG injection timing delay relative to the methanol injection timing can be optimized to ensure that most fuels enter into the cylinder in the injection cycle and the following cycle and that reliable ignition and combustion happen in the third cycle. Optimal control of the fuel injection timing and the LPG injection timing delay relative to the methanol injection timing improves firing performances. reduces the hydrocarbon and unburned methanol emissions during cold start, and increases formaldehyde emissions slightly. The variations in formaldehyde and unburned methanol emissions show opposite tendencies with the variations in methanol injection timing, the LPG injection timing, and the LPG injection timing delay relative to the methanol injection timing.