Date of Award
Doctor of Philosophy
Jon H. Van Gerpen
A phenomenological multizone transient spray model has been developed to simulate the performance and nitric oxide emission characteristics of a turbocharged diesel engine fumigated with alcohol. The effects of speed, load, alcohol proof, and the fraction of the engine's power supplied by the alcohol have been investigated. The multizone model is designed to account for the heterogeneous composition of the cylinder contents by dividing the cylinder into a number of smaller zones. Each of these smaller divisions is treated as being locally homogeneous. The model includes the interactions between the fuel spray and swirling air in the cylinder. The effect of wall impingement on the fuel-air mixing and combustion has been incorporated in the model. Correlations for spray geometry, fuel-air distribution in the spray plume, air entrainment, and heat transfer have been used to develop the model. A complete thermodynamic analysis has been applied to the individual zones to obtain cylinder pressure data. The indicated mean effective pressure and indicated thermal efficiency are derived from the pressure data. The exhaust temperature is estimated using a simple two-step blowdown and expansion process. The exhaust nitric oxide level is predicted by a chemical kinetic model applied to each individual zone;To validate the model, a four-cylinder turbocharged diesel engine was operated over a large matrix of different conditions. A mixture of alcohol and water was fumigated into the intake manifold after the turbocharger compressor. The engine was operated at two different speeds and four different load conditions. Varying amounts of alcohol were fumigated to replace 10, 20, 30, and 40% of the full load torque. Alcohol-water mixtures of varying proofs. between 40 and 169.5 proof, were tested. Comparisons were made between ethanol-water, and methanol-water mixtures on an equal energy basis that includes the enthalpy of vaporization of the alcohol and water. Tests with water injection into the intake manifold were also carried out to study the effect of water contained in the alcohol-water mixture on engine performance;The values of indicated mean effective pressure, indicated thermal efficiency, and exhaust temperature predicted by the model matched closely with experimental data. The general trends in the three parameters were also correctly predicted by the model. The exhaust nitric oxide emission predicted by the model matched reasonably well for diesel-only operation. With alcohol fumigation, the model overpredicts the reduction in nitric oxide. This is attributed to the inability of a single-zone wall impingement model to accurately simulate the temperature and composition of the regions where nitric oxide is formed.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Ottikkutti, Pradheepram, "Multizone modeling of a fumigated diesel engine " (1989). Retrospective Theses and Dissertations. 9161.