Multizone Modeling of a Fumigated Diesel Engine

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 locally homogeneous zones. The model includes the interactions between the fuel spray and swirling air in the cylinder and the effect of wall impingement on fuel-air mixing and combustion. 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 derived from the pressure data, estimated exhaust temperature, and the exhaust nitric oxide level are compared with data obtained from a four-cylinder turbocharged diesel engine over a wide range of operating conditions.

The values of indicated mean effective pressure, indicated thermal efficiency, and exhaust temperature predicted by the model matched closely with experimental data. 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 the single-zone wall impingement model to accurately simulate the temperature and composition of the regions within the wall zone where nitric oxide is formed.