Experimental Investigation of the Performance and Unburned Methanol, Formaldehyde, and Carbon Dioxide Emissions of a Methanol-Diesel Dual-Fuel Engine

Abstract

In the context of global efforts to pursue carbon neutrality, the methanol-diesel reactivity controlled compression ignition (RCCI) combustion has become a promising strategy for diesel engines to reduce emissions with higher thermal efficiency. To further improve the fuel economy of the methanol–diesel RCCI engine and reduce its unregulated emissions, the effects of methanol substitution rate (MSR) and exhaust gas recirculation (EGR) on fuel economy, CO2, MeOH, and H-CHO emissions at different engine speed and load conditions were tested. The conversion efficiency of a conventional diesel oxidation catalyst (DOC) in oxidizing the unregulated emissions under the World Harmonized Steady-State Cycle (WHSC) was also evaluated. The results showed that running the engine in methanol-diesel RCCI mode can significantly improve fuel economy at medium to high loads [greater than 1.18 MPa brake mean effective pressure (BMEP)]. The equivalent brake specific fuel consumption (ESFC) in the RCCI mode was lower than that of the baseline CDC mode, and the utilization of EGR can further improved fuel economy at lower load conditions. The MeOH and H-CHO emissions increased as the MSR increased, and they decreased as the load level and EGR rate increased. The CO2 emissions decreased as the MSR increased, but they increased as the EGR rate increased. The conversion efficiencies of DOC for MeOH, H-CHO and aromatic hydrocarbons (AHC) were around 93%, 84%, and 61%, respectively, under the WHSC test. Exhaust after-treatment by DOC is an effective solution to reduce unburned MeOH and H-CHO from methanol-diesel dual-fuel engines, and to extend RCCI operating range.