Experimental Investigation of Internal and External EGR Effects on a CNG-OME Dual-Fuel Engine 2024-01-2361

Dual-fuel engines powered by renewable fuels provide a potential solution for reducing the carbon footprint and emissions of transportation, contributing to the goal of achieving sustainable mobility. The investigation presented in the following uses a dual-fuel engine concept running on biogas (referred to as CNG in this paper) and the e-fuel polyoxymethylene dimethyl ether (OME). The current study focuses on the effects of exhaust gas rebreathing and external exhaust gas recirculation (EGR) on emissions and brake thermal efficiency (BTE).

A four-cylinder heavy-duty engine converted to dual-fuel operation was used to conduct the engine tests at a load point of 1600 min^-1 and 9.8 bar brake mean effective pressure (BMEP). The respective shares of high reactivity fuel (HRF, here: OME) and low reactivity fuel (LRF, here: CNG) were varied, as were the external and internal EGR rates and their combinations. CNG was injected into the intake manifold to create a homogeneous air-fuel mixture, while OME was introduced as a pilot injection directly into the combustion chamber. Results showed an increase in total hydrocarbons (THC) and carbon monoxide (CO) emissions, while nitric oxide (NOx) emissions were significantly reduced compared to diesel operation. Soot emissions were completely mitigated due to the absence of direct carbon bonds in both CNG and OME. For the initial stage of the study, exhaust gas rebreathing was implemented on only one exhaust valve through a second event lift. For the second part of the study, the second event lift was also installed on the other exhaust valve. At a substitution rate of 50 % CNG, THC emissions could be lowered by up to 35 %, CO emissions by up to 50 % and NOx emissions by up to 18 % with the use of internal EGR. The combination of internal and external EGR reduced emissions even further.