Greenhouse Gas Reduction via Co-optimization of Alternative Diesel Fuels with Compression Ignition Engines

Abstract

In this thesis, the co-optimization of three different alternative diesel fuels with conventional diesel engines is investigated as means to reduce greenhouse gas emissions from transportation sector. For the application of biodiesel in diesel engines, this thesis focuses on the impact of B20 and engine control unit (ECU) setting on the greenhouse gas and criteria pollutant emissions, and also focuses on the optimization of the ECU of a medium-duty diesel engine for B20 to minimize the greenhouse gas emissions. With the optimized ECU setting, B20 achieved relative 0.5% improvement in its tank-to-wheels (TTW) GHG emissions during the EPA FTP75 certification cycle. B20 also achieved 25.5% decrease in BSNOx and 16.7% decrease in BSPM emissions with the optimized ECU setting. The range of optimized ECU parameters and the engine operating conditions investigated in the current study is unprecedentedly comprehensive. For the application of dimethyl ether (DME) in compression-ignition engines, this thesis focuses on the optimization of the physico-chemical properties of the dimethyl ether (e.g., viscosity) to the existing diesel fuel injection system via glycerol blending. To prevent the phase separation between DME and glycerol, effective co-solvents are found using various selection criteria including co-solvent effectiveness based on Hansen Solubility Parameter theory, viscosity, oxygen content, health and environmental risks, and renewable production availability. Propylene glycol and di-propylene glycol are selected as the two final co-solvents, and are used to develop two different DME-glycerol blends. Those blends are named as Michigan DME I (i.e., mixture of DME, glycerol, and dipropylene glycol) and Michigan DME II (i.e., mixture of DME, glycerol, and propylene glycol). Both Michigan DME blends achieved No.2 diesel level viscosity (i.e., ~1.9cSt at 40ºC) with around 45 wt. % of DME without phase separation at ambient temperature (~20ºC). Both of the novel DME blends are expected to burn soot-free and are assessed to have about 50% reduction in well-to-wheels GHG emissions compared to the petroleum-derived diesel. For the application of jet fuels in diesel engines, this thesis focuses on the characterization of bulk modulus and speed of sound of the conventional and alternative jet fuels applicable to the U. S. Army ground vehicles equipped with pump-line-nozzle fuel injection system. The un-optimal operations of the fuel injection system due to the difference between the bulk modulus and speed of sound of jet fuels and petroleum-based diesel fuel were the motivation for this research. The bulk modulus and speed of sound of 3 different petroleum-based jet fuels and 3 different alternative jet fuels are measured and compared with each other. The rank order of bulk modulus and speed of sound were same: petroleum-based diesel > 3 petroleum-based jet fuels ≈ Farnesane > Hydrotreated Renewable Jet fuel derived from Camelina (HRJC) > Alcohol-to-jet (ATJ) fuel. Quantitatively speaking, the isothermal bulk modulus of the three petroleum-based jet fuels was 20-25% lower than that of the petroleum-based diesel due to the combined effect of lower aromatic content and lower carbon number of the major components of the petroleum-based jet fuels. Farnesane had similar isothermal bulk modulus to the three petroleum-based jet fuels while the HRJC had about 4% lower isothermal bulk modulus than Farnesane due to its lower carbon number. Alcohol-to-jet (ATJ) fuel had the lowest isothermal bulk modulus out of all measured fuels: 14% lower isothermal bulk modulus than Farnesane.