Emissions of Formaldehyde and Unburned Methanol from a Spark-Ignition Methanol Engine during Cold Start

The effects of the methanol injection quantity per cycle, the ignition timing, the methanol injection timing, the additional liquefied petroleum gas (LPG) injected into the inlet port, and the LPG injection timing delay relative to the methanol injection timing on the formaldehyde and the unburned methanol emissions from an electronically controlled inlet port methanol injection spark-ignition (SI) engine during cold start were investigated using a single-cycle fuel injection strategy. The results showed that the methanol injection quantity per cycle, the ignition timing, the methanol injection timing, the mass ratio of injected LPG/ methanol, and the LPG injection timing delay relative to the methanol injection timing affect the formaldehyde and the unburned methanol emissions significantly. Optimal control of the methanol injection quantity per cycle, the ignition timing, the methanol injection timing, and the LPG injection timing delay relative to the methanol injection timing improves firing performances and reduces the unburned methanol emission. As the mass ratio of injected LPG/methanol increases, the formaldehyde emission increases and the unburned methanol emission falls. The variations in emitted formaldehyde and unburned methanol show opposite tendencies with the variations in the methanol injection quantity per cycle, the ignition timing, the methanol injection timing, the mass ratio of injected LPG/methanol, and the LPG injection timing delay relative to the methanol injection timing.