Masters Theses

Date of Award

8-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

J. W. Hodgson

Committee Members

W. S. Johnson, Ke Nguyen, J. R. Parsons

Abstract

Due to an increasing threat of oil shortages and concerns about air quality, attempts have been made to reduce the United States' dependency on petroleum. Two possible solutions that have been receiving attention are to reduce the fuel consumption of modern automobiles and to use alternative fuels. This study considers both possibilities for a combined solution. To accomplish this, a stock gasoline vehicle was converted to operate on M85, a mixture of 85 percent methanol and 15 percent gasoline by volume, and concepts used to increase the vehicle's fuel economy were implemented in order to improve the conversion.

Under normal circumstances, a simple conversion of an engine, from gasoline to methanol operation, results in an increase in power-related performance. This increase is due to methanol's high latent heat of vaporization and low stoichiometric air/fuel ratio, which lead to increased volumetric efficiency. More complex conversions attempt to exploit methanol's high octane rating, which reduces the tendency for auto-ignition, through the use of turbo/superchargers and/or raising the compression ratio. For this study, it was desired to use these properties to increase the vehicle's fuel economy potential rather than its power-related performance. Therefore, the conversion was made such that the power-related performance of the developmental vehicle matched that of the baseline vehicle.

The properties of methanol mentioned above provide the opportunity to produce the same power-related performance of a gasoline engine from a smaller displacement methanol engine. Using this fact, the strategy selected was that of increasing the fuel economy potential through a reduction in the number of cylinders and thus the overall engine displacement. In order to reduce the number of variables changed and thus allow for a direct comparison of the developmental vehicle to the baseline vehicle, it was decided that the same engine, a Chevrolet 2.8 liter V-6, should be used for both the baseline and developmental vehicles.

The developmental engine's displacement was reduced to 1.9 liters by modifying two cylinders so that they did not fire, and therefore converting the engine into a V-4 configuration. The two "dead" pistons were left in the engine for balancing purposes. However, their contribution to the engine's overall friction was reduced by removing the piston rings, and their pumping work was reduced by cutting slots in the piston crowns such that the crankcase gases could flow freely around the piston. The developmental engine was then outfitted with a turbocharger in order that the engine's power-related performance would match that of the baseline engine. Other than the modifications described above and those required for the conversion from gasoline to methanol fuel, the developmental vehicle's configuration was the same as that of the baseline.

After implementing the above modifications, the vehicle underwent various tests to determine the success of the conversion. It was found that an approximate increase of 19 percent was experienced in the gasoline equivalent fuel economy over the federal test procedure city and highway emissions test cycles. It was also found that increases of up to 21 percent could be experienced at steady state highway speeds.

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