Investigation on Methanol Engine with DME Fumigation

Artikel i vetenskaplig tidskrift, 1999

Being a non-soot and low NOx emission level fuel, methanol (MeOH) might be considered as an attractive candidate for use in diesel engine. However, having low cetane number and high heat of vaporization, it is not possible to use in diesel engines without engine modifications. In order to take advantages of the alcohol fuels and to avoid engine complexities, which might come along with such modifications, the use of ignition improver additives dissolved in the base fuel is a normal practice. Another promising solution for qualitative combustion in methanol diesel engines is to design an onboard methanol dehydration reactor which can generate dimethyl ether (DME), for use as ignition improver. As a dissolved mixture MeOH-DME requires a special fuel system, the main emphasis was put on the fumigation technique, where a small quantity of DME has been injected into the inlet duct of the engine and the base fuel (MeOH) is conventionally injected through the common rail pump. A research program was set up for evaluating the effectiveness of DME as ignition improver and to compare results with the conventional additive poly-ethylene-glycol (PEG). The heat release analysis has shown that, the fumigated DME undergoes sufficient combustion during compression stroke. Consequently, the temperature and pressure of the gases in the cylinder increase to the point, where the ignition delay of the base fuel (MeOH) is very short. Such precombustion affects the engine performance and emission output, especially NOx and HC levels. It was generally observed that, the regulated emissions were lower and the engine efficiency slightly higher when compared with those obtained when ethanol (EtOH) mixed with PEG or EtOH with fumigated DEE were used. However, the fumigation tests have shown that running on MeOH fuel, the maximum torque and maximum power could not be reached, as it was expected, due to the limited delivery of flow from the fuel pump. Nevertheless, verified possibilities for using DME as ignition improver in a methanol diesel engine, leads to a proper version of the on-board DME reactor design, which would bring to another solution for methanol fuelled engines.