An examination of performance deterioration indicators of diesel engines on the plateau

This paper investigated the sensitivity of diesel engine performance to plateau environment. A three-dimensional computational fluid dynamics engine model validated against the experimental data was performed to provide analytical data from sea level to 5000 m at a constant engine speed and fuel injection strategy. The simulation results showed that the engine torque exhibited a nonlinear reduction with decreasing ambient pressure. Similarly, the fuel consumption increased non-linearly with altitude due to the combustion deterioration. However, the decline in the engine pressure-related parameters was smooth since flame extinction did not occur. As for nitrogen oxides emissions, high altitude operations steadily reduced the area of the thermal nitric oxide production zone, and therefore it decreased smoothly with altitude. In addition, soot emission levels rose with altitude mainly due to the reduced air utilization capacity, which boosted the soot formation while simultaneously undermined the percentage of soot oxidation. Soot concentrations suddenly increased when the engine was operated above ∼4000 m. This was due to the enhanced penetration of the diesel spray, which caused wall adhesion, adding another soot formation mechanism. As a result, soot is the appropriate indicator to find the maximum altitude that engine can tolerate without significant performance degradation.