The effects of the ambient temperature on the firing behavior and the unregulated emissions (formaldehyde and unburned methanol emissions) of electronically controlled inlet port injection spark-ignition methanol and liquefied petroleum gas (LPG)/methanol engines during the cold start were investigated experimentally by means of a single-cycle fuel injection strategy. The test results indicated that the minimum amount of methanol injected per cycle to ensure the methanol engine reliable firing increases 86% with the reduction of the ambient temperature from 301 to 289 K. With the ambient temperature below 289 K, the methanol engine cannot be started reliably without the other assistant measures even with a large methanol injection. The LPG only played a part of start-aids in the LPG/methanol engine. Using additional LPG injected into the inlet port results in a reliable firing of the LPG/methanol engine at low ambient temperature during cold start. When the ambient temperature drops, the mass ratio of injected LPG/methanol for the reliable firing of the LPG/methanol engine during cold start increases rapidly. The maximum combustion pressure in the cylinder, the maximum instantaneous engine speed, and the formaldehyde emissions increase significantly and the unburned methanol decreases obviously with the rise of the ambient temperature. (C) 2010 Elsevier Ltd. All rights reserved.