Study of cylinder-to-cylinder variation in a diesel engine fueled with diesel/methanol dual fuel

• The UED of engine increases with the MSP under various engine loads.
• The MSP within 40% is preferable.
• It is helpful to decrease the UED as intake air temperature within 35–80 °C.
• Increasing of engine speed can decrease cylinder-to-cylinder variation and UED.

The methanol fuel used in diesel engine can reduce the emissions effectively, while the performance of engine keeps unchanged or even improved, the study of methanol used in diesel engine is paid more and more attention. Experiments were conducted in a 4-cylinder, turbocharged direct injection diesel engine fueled with diesel/methanol dual fuel (DMDF). In the experiment, methanol was injected into inlet duct by two low-pressure injectors, and directly mixed with intake air before entering the engine. The diesel fuel was directly injected in cylinder. The methanol substitution percent (MSP), intake air temperature and engine speed were changed to investigate the unevenness degree (UED) cylinder-to-cylinder. The experimental results show that the UED of engine increases with the increase of MSP under various engine loads, the COVpp increases with MSP under low engine load, and the COVpp curves vary very little under low MSP under 75% and 100% engine load, but a significantly rise appeared when MSP further increases. The UED gradually increases with the increase of intake air temperature, and it is usually less than 8% when intake air temperatures lower than 80 °C under 40% MSP. It suggests it is helpful to decrease the UED when the intake air temperature is in the range of 35–80 °C as MSP less than 40%. In addition, the difference of pressure between cylinder-to-cylinder decreases with the increase of engine speed, it can be considered raising MSP at high engine speed in order to gain better engine economy.