Investigation on the regulated and unregulated emissions of a DME engine under different injection timing

In this study, a two-cylinder, direct injection compression ignition engine was retrofitted to run on dimethyl ether (DME) fuel. Under different fuel delivery timing, total hydrocarbon (THC), carbon monoxide (CO), nitrogen oxides (NOx), smoke, DME and formaldehyde (CH2O) emission characteristics of DME engine were investigated and compared with diesel engine. A gas chromatograph with pulsed discharge helium ionization detector (PDHID) was applied to measure the exhausted DME and CH2O, and the regulated emissions were detected with MEXA 7100 DEGR, Horiba. The measurement proved that DME and CH2O are the main components of THC emission from DME engine. And, for the reason that these two emissions are normally less responded by flame ionization detector (FID), the DME engine THC emission of FID should be corrected. Compared with diesel engine, DME engine can achieve smoke-free and significant lower THC and NOx emissions. CO emission of DME engine is decreased at low and middle engine speed conditions as well. CH2O emissions for both fuels are approximately equal. Retarding DME injection timing, NOx emission can be further reduced, while the increase of CO, THC, DME and CH2O emission are observed.