Abstract
A way to reduce net CO2 emission and circumvent the high particle emissions from compression ignition (CI) engines, while retaining high efficiency, is by utilizing lighter alcohols in the partially premixed combustion (PPC) process. Methanol and ethanol have a very short carbon chain, and form less soot/particulate matter (PM) during combustion compared to diesel fuel. This study analyzes and compares the characteristics of PM emissions from methanol, ethanol and diesel in terms of soot mass concentration, number concentration and particle size distribution in one cylinder of a six cylinder Scania D13 heavy duty (HD) engine under two operating loads; 6 bar and 10 bar gross mean indicated effective pressure (IMEPG). An electrostatic precipitator (ESP) was used to sample PM on copper grids for transmission electron microscopy (TEM) and energy dispersive X-ray analysis. Also, new and used lubrication oil together with methanol and diesel were analyzed for their sulphur and metal content.
Nucleation mode and the majority of accumulation mode particles from methanol and ethanol combustion, showed mainly Ca, S, P and Zn in the energy dispersive X-ray spectrometry (EDX) analysis and were hypothesized to be emitted mainly from the lubrication oil rather than the combustion of the fuel itself. From diesel combustion, the accumulation mode particles were more abundant in comparison with the alcohols and PM/soot emissions measured with the photoacoustic technique were 3 to 10 times higher than for the alcohols. There were also fewer nucleation mode particles present; although they consisted of the same four abovementioned elements. Utilizing alcohols in CI engines have a great advantage regarding PM, particle number emissions and efficiency. However, the resulting nucleation mode particles need to be reduced to avoid future health concerns.
