Study of the characteristics of PM and the correlation of soot and smoke opacity on the diesel methanol dual fuel engine

Methanol is regarded as an alternative fuel of diesel for reducing the particulate matter emissions on diesel engines. However, recent studies reveal that methanol has the different effects on particulate matter characteristics at high loads. In order to reduce particulate matter emissions further within the full operating range of the engine, the characteristics of particulate matter and the correlation between soot and smoke opacity were investigated on a turbocharged and intercooled diesel engine under diesel/methanol dual fuel mode. During the experiment, particulate characteristics are primarily exhibited by the characteristics of soot and particulate number. Results show that the engine-out soot and particulate number emissions increase with the increase of methanol substitution percent under high intake temperature at high loads. On the contrary, the engine-out soot and particulate number decrease with the increase of methanol substitution percent under low intake temperature at high loads. There is an applicable scope of methanol substitution percent that effectively reduces soot and particulate number emissions. Methanol substitution percent which is larger than 20% has a significant effect on the decrease of soot and particulate number. At low and medium loads, the effect of methanol substitution percent on soot and particulate number emissions is dependent on the start of injection. The effect of methanol substitution percent on the decrease of particles strengthens as the start of injection is away from the top dead center. The inflection point of particulate number and soot emissions moves forward with the increased methanol substitution percent. Compared to pure diesel mode, the strong correlation between soot and smoke opacity does not exist on diesel/methanol dual fuel mode. However, the correlation between soot and smoke opacity comes back in usage of the diesel oxidation catalyst or exhaust gas recirculation on diesel/methanol dual fuel mode. Most of nitrogen dioxide and unburned hydrocarbons are reduced by the diesel oxidation catalyst on diesel/methanol dual fuel mode.