Performance and Emission Characteristics of DME Engine with High Ratio of EGR

The combustion of dimethyl ether (DME) fuel, due to its simple chemical structure and high oxygen content, produces less exhaust gaseous products such as HC, CO and NOx. Moreover, soot-free combustion can be observed under all of the operating conditions, which allows a high ratio of exhaust gas recirculation (EGR) for NOx reduction without being restricted by the NOx-soot tradeoff. The effects of a high ratio of exhaust gas recirculation on performance and exhaust emissions from a DME engine were investigated. The results showed that EGR ratio has significant effects on power output and fuel consumption. NOx emission is considerably reduced with the decrease of oxygen concentration, and a higher level of EGR results in a greater reduction in NOx emission. Ultralow NOx emissions have been realized under a high ratio of EGR operations, however, accompanied with the increase of HC and CO emissions. High EGR ratios need to be applied under low loads, but low EGR ratios are sufficient for high loads. Considering all of the operating conditions, optimized EGR ratios were selected, and the tests were conducted under the European Steady-State Test Cycle. As expected, NOx emissions from a DME engine can easily meet the Euro IV limit with optimized EGR ratios.