Methanol Evaporation in an Engine Intake Runner under Various Conditions

Methanol has recently emerged as a promising fuel for internal combustion engines due to its multiple carbon-neutral production routes and advantageous properties when combusting. Methanol is intrinsically more suitable for spark-ignition (SI) operation thanks to its high octane number, but its potential in heavy-duty applications also encourages engine manufacturers in this field to retrofit their existing compression-ignition products into methanol/diesel dual-fuel (DF) operation. For both SI operation and DF operation, injecting methanol into the engine’s intake path at low pressure is a relatively simple and robust method to introduce methanol into the cylinders. However, the much higher heat of vaporization (HoV) of methanol compared to conventional SI fuels like gasoline can be a double-edged sword. On the one hand, its enhanced cooling effect may increase volumetric efficiency and lower knock tendency, on the other hand, the extra heat it absorbs when evaporating may pose cold-start issues and lead to unstable combustion. To further investigate, a special experimental setup was built. Multiple thermocouples were mounted on an intake runner where the fuel is injected to monitor the temperature changes of the flow before and after injection. The temperature of the runner itself was also monitored to assess the heat taken from the metal wall of the runner pipe. Different air-fuel ratios, air temperatures, air pressures, and air mass flow rates were tested to evaluate their influences on methanol evaporation. The test results were then compared with conventional gasoline operation. It was found that the temperature drop after fuel injection is strongly dependent on the flow temperature, and that the evaporated fraction of methanol was far lower than that of gasoline even with higher flow temperature. Their very different evaporation behaviors are thoroughly discussed.