DME as an Alternative Fuel for Compression Ignition Engines in Long-Haul Heavy-Duty Transport

For long-haul heavy-duty transport, ICE (Internal Combustion Engine) propulsion will continue to play a dominant role. Fossil Diesel fuel with its high energy density, even made of biogenic or synthetic source, will not remain the prime and cost-efficient solution under always more stringent emission limits for greenhouse gas and pollutants. Our assessment of all relevant alternative fuels from renewable source resulted in DME (Dimethyl-ether) being the most promising fuel for long-haul applications. DME shows one of the best compromises regarding energy density, emission reduction potential and production cost. In particular, DME fuel in a compression ignition engine achieves similar thermal efficiency as a diesel fuel but with significantly lower CO2 emissions (TtW) due to the favourable H/C ratio and potentially down to zero (WtW) if produced from bio- or renewable sources. DME is nowadays already industrially produced in large quantities from Methanol as an intermediate in a very low-loss catalytic process. The aim of the funded project led by FPT was to demonstrate this promising potential by experimental test with a typical engine for long-haul applications (11 litre Diesel engine with 338 kW / 2300Nm) including some specific modifications to be able to run with DME as well as a new approach for provicing EGR using a volumetric EGR pump. For correct comparison, the same engine has been run for base mapping with diesel fuel before changing only the DME related parts like high pressure pump and injectors. The rest of the HW structure remained untouched. Intensive CFD simulations were carried out to optimise the combustion chamber. The experimental results confirmed the CO2 reduction potential. Brake thermal efficiency (BTE) was on the same level as Diesel or slightly higher depending on engine-out NOx level while soot emissions remained at zero independently of NOx engine-out level. It was crucial to demonstrate very low engine out NOx and no soot emissions with still good thermal efficiency for thermal management during cold phase. This could also imply less sophisticated exhaust after-treatment systems considering future emission legislation like i.e. Euro VII. Specific HC species like DME have been measured in the exhaust as well as N2O and Particulate Numbers (PN). All of them could be identified to be far below critical limits.