Impact of diesel-hythane dual-fuel combustion on engine performance and emissions in a heavy-duty engine at low-load condition

Abstract

Heavy-duty diesel vehicles are currently a significant part of the transportation sector, as well as one of the major sources of carbon dioxide (CO2) emissions. International commitments to reduce greenhouse gas (GHG) emissions, particularly CO2 and methane (CH4) highlight the need to diversify towards cleaner and more sustainable fuels. Hythane, a 20% hydrogen and 80% methane mixture, can be a potential solution to this problem in the near future. This research was focused on an experimental evaluation of partially replacing diesel with hythane fuel in a single-cylinder 2.0 L heavy-duty diesel engine operating in the diesel-gas dual fuel combustion mode. The study investigated different gas substitution fractions (0%, 38% and 76%) of hythane provided by port fuel injections at 0.6 MPa indicated mean effective pressure (IMEP) and a fixed engine speed of 1200 rpm. Various engine control strategies, such as diesel injection timing optimisation, intake air pressure and exhaust gas recirculation (EGR) were investigated in order to optimise the dual-fuel combustion mode. The results indicated that by using hythane energy fraction (HEF) of 76% combined with 125 kPa intake air boost and 25% EGR dilution, CO2 emissions could be decreased by up to 23%, while indicated thermal efficiency (ITE) was compromised by 1.5 percentage points, equivalent to a 3% reduction. Furthermore, soot was maintained below Euro VI limit and nitrogen oxides (NOx) level was held below the Euro VI regulation limit of 8.5 g/kWh assuming a NOx conversion efficiency of 95% in a selective catalyst reduction (SCR) system. Nevertheless, carbon monoxide (CO), unburned hydrocarbon (HC) and methane slip levels were considerably higher, compared to the diesel-only baseline. The use of a pre-injection prior to the diesel main injection was essential to control the heat release and pressure rise rates under such conditions.