1990-02-01

Warmup Characteristics of a Spark Ignition Engine as a Function of Speed and Load 900683

The warmup characteristics of an engine have an important impact on a variety of design issues such as performance, emissions and durability. A computer simulation has been developed which permits a detailed transient simulation of the engine warmup period from initial ambient conditions to a fully warmed up state. The simulation combines a detailed crankangle-by-crankangle calculation of in-cylinder processes and of engine air flow, with finite element heat conduction calculations of heat transfer from the gases, through the structure to the coolant. The paper describes one particular application of the simulation to the warmup of a 2.5ℓ spark ignited engine from cold start to a fully warmed up state at several speeds ranging from 1600 to 5200 rpm and loads ranging from 25% to 100% at each speed. The response of structure temperatures, charge temperature at IVC and of the exhaust temperature has been calculated and is documented in terms of characteristic warmup times.
ENGINE WARMUP from cold start is one of the critical periods in engine operation. It is during this period, that engines emit the largest fraction of unburned hydrocarbons, experience significant cylinder wear, have high cylinder gas blowby, and fuel economy is negatively affected by high friction and by rich operation needed to overcome poor combustion. (A separate, but related issue, is the time required for engine response to throttle changes.) A variety of key design issues are thus related to this operating period, and much developmental time is devoted to controlling the adverse impact of warmup.
This developmental effort can be assisted by means of a computer simulation which can represent in detail the heat transfer process in an engine, including the transient aspects such as thermal inertia of the engine structure. The simulation also has to have the capability to represent the processes affected by the warmup, such as piston/ring/cylinder tribology, charge temperature, turbocharger dynamics, blowby, and component distortion. This paper describes the progress made in the development of such a simulation and illustrates its use on an application to a spark ignited engine.

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