Effects of injection timing of methanol and LPG proportion on cold start characteristics of SI methanol engine with LPG enriched port injection under cycle-by-cycle control

A liquefied petroleum gas (LPG) enriched port injection start aid was used to improve firing and emissions characteristics and overcome cold start difficulties for spark ignition (SI) methanol engines at low ambient temperature. The effects of injection timing of methanol and LPG addition fraction on cold start firing; and hydrocarbon (HC), formaldehyde, and unburned methanol emissions were investigated experimentally using cycle-by-cycle control strategy. Injection timing of methanol significantly affected cold start firing behavior for constant injection timing of LPG. At optimal injection timing of methanol the most fuels enter into the cylinder on time to realize ideal firing of the next cycle combustion after fuel injection. Sufficient LPG addition can ensure reliable cold start firing. The methanol engine obtained lowest HC and unburned methanol, and highest formaldehyde tailpipe emissions for optimal injection timing of methanol. Increasing LPG addition fraction significantly decreased HC and unburned methanol tailpipe emissions and increased formaldehyde emission rapidly. Formaldehyde and unburned methanol tailpipe emissions showed opposite tendencies with injection timing of methanol and LPG addition fraction, whereas HC and unburned methanol tailpipe emissions showed similar tendencies during cold start.