Simulation of an Intake Manifold Pre-Heater for Cold Engine Startup

Ensuring consistent, reliable diesel engine startups in cold temperatures is of utmost importance in a number of applications. Under extreme temperatures, the use of glow plugs is complemented by intake manifold heaters. In these, the energy released from combustion increases the intake air temperature before the air enters the main combustion chamber. Since the process also alters the stoichiometry of the fuel-air mixture at the intake ports, the pre-heater operation must be optimized in order to guarantee successful and reliable in-cylinder combustion during engine startups. This paper describes the development of an intake manifold model incorporating an air pre-heater for application in a diesel engine. The model, created using a commercial one-dimensional simulation tool, was validated against experimental data and subsequently used to quantify the concentration of combustion product species at the intake runners, as well as intake charge dilution. Results showed that the effective equivalence ratio might increase up to 2.6 after the first 25 seconds of cranking, with 12.5% reduction of the O₂ concentration in the intake charge.