Effect of altitude on thermal balance of a heavy-duty diesel engine

Diesel engines working at high altitudes are prone to thermal failure. In this paper, a series of experiments and simulations were conducted to analyze the thermal balance, incylinder heat transfer, and performance of diesel engines at various altitudes. A six-cylinder four-stroke diesel engine was used to conduct the thermal balance tests at altitudes from 0 m to 4500 m. The experiment results show that the engine thermal efficiency declines from 37.8% to 33.9% at the rated speed as altitude rises. The heat loss through cooling water has no significant change in trend and remains about 22%-24% in most conditions. The heat loss through exhaust decreases as altitude rises and accounts for 26.7%-39.8% of total energy. The unaccounted losses increase greatly as altitude rises but it makes up no more than 12.1% of total energy at all altitudes. To acquire more detailed in-cylinder heat transfer parameters, a one-dimensional in-cylinder simulation was conducted. The simulation results show that the in-cylinder heat transfer coefficient and heat fluxes increase first and then decrease as altitude rises. In addition, with the increase of altitude, the in-cylinder average gas temperature substantially increases. This study has practical significance for reducing thermal load of the engines working at high altitudes.