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Today, nearly half of the world population lives in urban areas. As the world population continues to migrate to urban areas for increased economic opportunities, addressing personal mobility challenges such as air pollution, Greenhouse Gases (GHGs) and traffic congestion in these regions will become even a greater challenge especially in rapidly growing nations. Road transportation is a major source of air pollution in urban areas causing numerous health concerns. Improvements in automobile technology over the past several decades have resulted in reducing conventional vehicle tailpipe emissions to exceptionally low levels. This transformation has been attained mainly through advancements in engine and transmission technologies and through partial electrification of vehicles. However, the technological advancements made so far alone will not be able to mitigate the issues due to increasing GHGs and air pollution in urban areas.

Fuel alcohols, such as M85 (a blend of 85 percent by volume methanol with hydrocarbons) and Ed85 (a blend of 85 percent by volume denatured ethanol with hydrocarbons), are inherently involatile at low temperatures and may contain soluble or insoluble contaminants. We explored the adequacy of existing specifications for M85 and Ed85 by studying fuel effects on cold starting and vapor flammability, and fuel contaminant effects on materials compatibility and filter plugging. These studies demonstrated deficiencies in existing specifications. Therefore, we developed General Motors specifications for M85 and Ed85 to improve vehicle performance and durability. Key features include a Cold Starting Performance Index to improve wintertime starting, a conductivity and chloride ion specification to reduce corrosion, and a particulate contamination limit to reduce filter plugging.

This paper documents the effects of primer composition and concentration on cold starting of 3.1L variable fuel vehicle (VFV) engines with fuel methanol. Primers were restricted to two commercially viable types: full boiling range gasolines and light isocrackate (LIC). Results show that cold starting performance improved with increasing pentane:butane ratio in fuels of equivalent RVP, and improved with increasing primer content. Cold starting performance showed an excellent correlation with vapor-air equivalence ratio (Фfv) and with initial liquid mass fraction of butanes and pentanes; the correlation between cold starting performance and fuel RVP was p.

Spark ignition engines are shown to have difficulty starting on high methanol-content fuels not only because of low fuel volatility but also because of electrical shorting of the ignition by methanol on the spark plugs. Using a concerted approach in which the fuel and ignition systems are optimized for fuel methanol, we have cold started a 2.5L spark ignition engine with port fuel injection down to -29°C on a 10.5 psi Reid vapor pressure M-85 (85% methanol, 15% gasoline). To minimize the amount of spark plug wetting, an exponential decay fuel algorithm is used which quickly generates flammable vapor mixtures while limiting the cylinder wetting. To overcome the spark plug wetting which does occur, ignition systems are used which have peak delivered currents twice as high as present-day automotive inductive ignitions.

Methanol, a popular alternative fuel candidate, can theoretically be dissociated on-board a vehicle into a 2/1 molar mixture of hydrogen (H2) and carbon monoxide (CO) having a 14 percent greater heating value than that of methanol vapor. In this study, engine efficiency and fuel consumption with methanol vapor and dissociated methanol (simulated by a 2/1 mixture of Ha and CO) were compared in a single-cylinder engine at equivalence ratios (Φ’s) ranging from 0.5 to 0.9 and compression ratios (CR’s) from 11 to 14. Whan compared at the same Φ and CR, the reduction in fuel consumption for dissociated methanol compared to methanol (3-7 percent) was smaller than would be expected based on heating value alone. Indicated thermal efficiency with dissociated methanol was only 0.89-0.55 times that with methanol. Thermodynamic analyses were conducted to isolate the factors responsible for lower efficiency with dissociated methanol.

Pure ethanol is being used as a spark-ignition engine fuel in Brazil, and is being considered for use in the U.S. and elsewhere. Efficiency and exhaust emissions with ethanol were quantified using a single-cylinder engine at compression ratios from 7.5 to 18, at equivalence ratios from 1.2 (rich) to the lean limit, and at MBT spark timing. Results were compared to those with gasoline at 7.5 compression ratio. With ethanol, compared to gasoline at the same compression ratio, engine thermal efficiency increased 3 percent, peak nitrogen oxide emissions decreased 40 percent, unburned fuel and carbon monoxide emissions were similar, and aldehyde emissions increased 110-360 percent. Increasing compression ratio from 7.5 to 18 with ethanol increased efficiency 18 percent, peak nitrogen oxide emissions 30 percent, unburned fuel emissions 25-200 percent, and aldehyde emissions 50-140 percent.

One of the reasons methanol is considered an attractive alternative fuel for automobiles is its high octane quality, which may allow the use of high compression ratio (CR) engines. To evaluate compromises between engine efficiency and exhaust emissions, a methanol-fueled single-cylinder engine was run at CR's from 8 to 18. At each CR, engine speed and airflow were constant at 1200 rpm and about half throttle, respectively; equivalence ratio (ø) was varied from 0.7 to 1.1; and spark timing was varied from best power (MBT) to 10° retarded. Knock was observed only at CR = 18 with MBT spark timing. Increasing CR from 8 to 18 while maintaining MBT spark timing increased efficiency about 16 percent, but also increased NOx and unburned fuel (UBF) emissions. Some previous studies have reported decreased NOx emissions with increased CR, possibly because MBT spark timing was not maintained.