A. S. Cheng

Investigation of the impact of biodiesel fuelling on NOx emissions using an optical direct injection diesel engine

Abstract The impact of biodiesel fuelling on NO x emissions was investigated using an optically accessible diesel engine. A soy-based biodiesel (B100) and three separate primary reference fuel (PRF) blends were evaluated over a range of loads at an engine speed of 800 r/min. Experimental operating conditions were carefully controlled to maintain a constant start of combustion (SOC), and a PRF blend was identified that would eliminate differences in premixed-burn fraction. A load-averaged NO x increase of ∼10 per cent was observed for B100 relative to the PRF blend with matched premixed-burn fraction. The results indicate that factors other than SOC and premixed-burn fraction affect the tendency for biodiesel to increase NO x . Equilibrium calculations reveal no significant differences in stoichiometric adiabatic flame temperature between the test fuels; however, experimental data suggest that actual flame temperatures may be influenced by differences in soot radiative heat transfer. The effect of biodiesel on mixture stoichi-ometry at the lift-off length may also play an important role in increasing NO x emissions.

The Effect of Oxygenates on Diesel Engine Particulate Matter

A summary is presented of experimental results obtained from a Cummins B5.9 175 hp, direct-injected diesel engine fueled with oxygenated diesel blends. The oxygenates tested were dimethoxy methane (DMM), diethyl ether, a blend of monoglyme and diglyme, and ethanol. The experimental results show that particulate matter (PM) reduction is controlled largely by the oxygen content of the blend fuel. For the fuels tested, the effect of chemical structure was observed to be small. Isotopic tracer tests with ethanol blends reveal that carbon from ethanol does contribute to soot formation, but is about 50% less likely to form soot when compared to carbon from the diesel portion of the fuel. Numerical modeling was carried out to investigate the effect of oxygenate addition on soot formation. This effort was conducted using a chemical kinetic mechanism incorporating n-heptane, DMM and ethanol chemistry, along with reactions describing soot formation. Results show that oxygenates reduce the production of soot precursors (and therefore soot and PM) through several key mechanisms. The first is due to the natural shift in pyrolysis and decomposition products. In addition, high radical concentrations produced by oxygenate addition promote carbon oxidation to CO and CO2, limiting carbon availability for soot precursor formation. Additionally, high radical concentrations (primarily OH) serve to limit aromatic ring growth and soot particle inception.

Methylal and Methylal-Diesel Blended Fuels for Use in Compression-Ignition Engines

Gas-to-liquids catalytic conversion technologies show promise for liberating stranded natural gas reserves and for achieving energy diversity worldwide. Some gas-to-liquids products are used as transportation fuels and as blendstocks for upgrading crude derived fuels. Methylal (CH{sub 3}-O-CH{sub 2}-O-CH{sub 3}) also known as dimethoxymethane or DMM, is a gas-to-liquid chemical that has been evaluated for use as a diesel fuel component. Methylal contains 42% oxygen by weight and is soluble in diesel fuel. The physical and chemical properties of neat methylal and for blends of methylal in conventional diesel fuel are presented. Methylal was found to be more volatile than diesel fuel, and special precautions for distribution and fuel tank storage are discussed. Steady state engine tests were also performed using an unmodified Cummins 85.9 turbocharged diesel engine to examine the effect of methylal blend concentration on performance and emissions. Substantial reductions of particulate matter emissions h ave been demonstrated 3r IO to 30% blends of methylal in diesel fuel. This research indicates that methylal may be an effective blendstock for diesel fuel provided design changes are made to vehicle fuel handling systems.

Quantifying the contribution of lubrication oil carbon to particulate emissions from a diesel engine

The contribution of lubrication oil to particulate matter (PM) emissions from a Cummins B5.9 Diesel engine was measured using accelerator mass spectrometry to trace carbon isotope concentrations. The engine operated at fixed medium load (285 N-m (210 ft.lbs.) 1600 m) used 100% biodiesel fuel (B100) with a contemporary carbon-14 ({sup 14}C) concentration of 103 amol {sup 14}C/ mg C. The C concentration of the exhaust C02 and PM were 102 and 99 amol {sup 14}C/mg C, respectively. The decrease in I4C content in the PM is due to the consumption of lubrication oil which is {sup 14}C-free. Approximately 4% of the carbon in PM came from lubrication oil under these operating conditions. The slight depression in CO{sub 2} isotope content could be attributed to ambient CO{sub 2} levels and measurement uncertainty.