Masters Theses

Date of Award

3-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Jeffery W. Hodgson

Committee Members

P. E. George, R. J. Krane, H. J. Wilkerson

Abstract

Recent concern over Iceland's dependence on imported oil products has brought new emphasis on synthetic nonpetroleum fuels such as hydrogen, methanol, and anhydrous ammonia. This study was undertaken to document the performance of a compression ignition engine fueled with anhydrous ammonia; and, to derive a mathematical model to predict the general behavior of anhydrous ammonia as a com pression engine fuel.

The engine used. Caterpillar D330c, 4 cylinder, 425 cu in, equipped with 17.5:1 compression ratio and precombustion chambers was not in any way modified to accommodate the unique combustion properties of the ammonia.

All tests were conducted with the engine running at the speed of 1500 rpm. Fuel-oil fueled engine tests were conducted to establish the baseline performance. Among results established for different engine loads were: the relationship between the fuel-oil and ammonia consumption; the thermal efficiency of the engine running for variable ammonia consumption; and, the relationship between induction air and ammonia consumption. Pressure-traces from the engine cylinder were also obtained.

The main findings of this study were that only moderate amounts of ammonia could be substituted for the fuel-oil. The limiting factor is the high rate of pressure rise in the cylinder, which in some cases was as high as 200 psi/deg. It is believed that this high rate of pressure increase is caused by abnormally high rate of release of chemical energy. It is shown that in order to secure satisfactory operation of the engine the rate of pressure increase should not exceed 90 psi/deg, during combustion. The thermal efficiency at full load increased slightly, 3%, with increases in ammonia consumption, but at low loads the thermal efficiency decreased by as much as 35%.

No emission tests were conducted, but it is estimated that as much as 40% of the ammonia consumed by the engine is not burned.

A mathematical model based on the constant volume combustion cycle was derived. The model was then used to predict the behavior of performance factors with increasing fractions of ammonia in the fuel-air mixture.

Results of the calculations are presented in the form of graphs. Results of this model indicate that for low ammonia fueling (0-25% by weight) the performance factors of the engine should not deviate significantly from those obtained with fuel-oil. This was substantiated by the experiment. However, for higher ammonia fueling rates the difference becomes significant. Because of the limited amount of fuel-oil that could be replaced by the ammonia, the ability of the mathematical model to predict the performance of the engine for higher ammonia fueling rates could not be fully investigated experimentally.

It is believed that the abnormal rate of pressure increase is caused by the exothermic reaction between the fuel and the oxygen, which in turn is caused by heterogeneous combustion of the ammonia within the cylinder. Therefore, it is proposed that future work be aimed toward investigating the combustion mechanics of the ammonia-air mixture within the cylinder. Also, means by which more regular combustion of the ammonia-air mixture can be achieved should be investigated.

In addition, since it is known that the combustion properties of ammonia are greatly improved by enriching the ammonia-air mixture with hydrogen, it is proposed that the possibilities of partially dissociating the ammonia outside the engine should be investigated.

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