Masters Theses

Date of Award

8-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Jeffrey W. Hodgson

Committee Members

Majid Keyhani, W. S. Johnson

Abstract

Currently several fuels are being viewed as possible alternatives to gasoline for use in motor vehicles and according to some authorities, methanol is the leading alternative fuel candidate. Although methanol is well suited for use in spark ignition engines, it is not an ideal fuel as there are problems associated with its use that require engineering solutions. The problems of specific interest to this study are poor cold starting and poor warm-up driveability. These low temperature problems are more apparent using methanol than gasoline due to methanol's higher latent heat of vaporization, lower stoichiometric air-fuel ratio and lower vapor pressure.

Solutions to these problems have been proposed and explored with varied success and this study examines still another possible cold start solution. This solution is based on the concept that if part of the methanol fuel could be burned in the intake air, the energy released would serve to heat the intake air stream. The heated air would then pass into the cylinder and result in increased cylinder compression temperatures, increased fuel vaporization and thus a better chance of in-cylinder combustion. Since the amount of fuel required to produce a 100°F temperature increase is very low, only small amounts of the oxygen in the intake air would be consumed to produce the heating effect.

To examine this concept, a methanol fueled burner/air heater was designed and installed in the air intake region of a test vehicle. This burner combusted a liquid methanol spray in a diffusion flame and confined the flame within a combustion can through the use of flame arrestors. This burner was designed for good air mixing while still maintaining control over the flame and was tested at temperatures as low as -12°F (lowest available test temperatures). Operation of the burner resulted in substantial air temperature increases within very short time periods, but was ineffective due to the large thermal capacity of the cold air intake manifold walls and cold engine parts. It was discovered that almost all of the energy released by the burner was dissipated to the cold engine before reaching the cylinders. A heat transfer analysis, performed for engine cranking conditions, showed that a burner exit temperature of over 3500°F would be required to overcome this large heat loss. This air temperature increase corresponds to an energy addition of 1980 BTU/min. An adiabatic flame temperature analysis showed that if all the intake air were stoichiometrically combusted in the burner/air heater a resulting air temperature of less than 3450°F would be achieved. In order to produce this temperature, which is below the desired air temperature, all of the intake air's oxygen would be consumed leaving none for in- cylinder combustion. Due to this, it was concluded that the thermal capacity of the cold engine was too much for this methanol fueled burner/air heater to overcome. The knowledge gained through this study have led to recommendations for possible future studies.

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