Alcohol Flexible Dual-Fuel Direct Injection Engine

Doktorsavhandling, 2020

Laws concerning emissions from HD internal combustion engines are becoming increasingly stringent in terms of local emissions and emissions concerning global warming such as lowering tailpipe CO2. New engine technologies are needed to satisfy these new requirements and to reduce fossil fuel dependency and increase renewable fuels in the transportation sector. One way to achieve both objectives can be to partially replace fossil fuels with alternatives that are sustainable with respect to emissions of greenhouse gases and engine out particulates. Also a decrease in NOx can be achieved. Suitable candidates are ethanol or methanol.


The thesis presented here summarizes results from publications and additional results presented here with the aim to investigate the possible advantages of combusting low carbon alcohol fuels in dual-fuel configuration in a HD Diesel engine - in particular, the potential to greatly reduce particulate emissions and thereby bypass the soot-NOx tradeoff and lowering tailpipe CO2 emissions. It was complimented by additional results presented in the kappa itself.


Ethanol sprays were studied in a high pressure/temperature spray chamber at typical engine condition with gas densities of about 27 kg/m^3 at around 550 C and around 60 bar. Spray parameters, such as the liquid cone angle, liquid penetration length and vapor penetration at injection pressures up to 2200 bar, were investigated. The characterization of those sprays was followed by an investigation focusing on the combustion of alcohol fuels in a single cylinder engine. Methanol, ethanol and E85 were chosen, but because of their poor auto-ignition properties, a pilot Diesel injection was used to initiate the combustion process. One of the alcohol fuels and Diesel were injected directly but separately, necessitating the use of two separate common rail systems together with a newly designed cylinder head and adapted injection nozzles. The dual fuel system's combustion properties were compared to those of pure Diesel with the same dual injection strategy. The injection pressure on the alcohol side were varied up to 2000 bar and investigations were carried out at low, medium and high speed-load points, with and without EGR. The investigated low carbon fuels outperformed Diesel under all tested conditions in terms of thermal efficiency and indicated specific NOx, soot and CO2 emissions. Thermal efficiency was increased by up to 3.5 %-points and simultaneously soot emissions were lowered by a factor of 40 or more and NOx by 20 %. ISCO2 emissions were down by up to 25 %. The fuel substitution ratio was over 95 % and the combustion stability was not compromised.