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A system-level, data driven model was developed to predict gas temperature in the exhaust manifolds of naturally aspirated spark ignited engines during vehicle operation. The model is based on data gathered from 67 vehicle tests. The data were collected over the last few years, from a dozen cars and trucks, spanning a range of rated power from 127 to 350 hp, engine displacements from 2 to 8 liters, Line-4, V-6 and V-8 engine configurations, vehicle mass from 1500 to nearly 9000 kg, trailer mass from zero to nearly 4000 kg, different vehicle drive schedules, different vehicle speeds, varying road grades up to a maximum in excess of 9% and ambient temperatures of 40°C. The large number of engine and vehicle design and operational variables that can influence exhaust gas temperature was limited to high-level variables known early in a vehicle development program.

A transient, one-dimensional, two-phase (crankcase gases and liquids) flow network model was developed (and coded in FORTRAN) to calculate the crankcase pressures versus crank angle during engine operation and the consequent crankcase pumping mean effective pressure (CPMEP). The two-phase flow was represented by an empirical expression. Note, CPMEP is one of the components of engine FMEP (friction mean effective pressure) and is being introduced here as a new term. The model was calibrated with engine crankcase pressure measurements. The motivation for the present work was the fact that no commercial (or public domain) software is available to adequately address this subject in sufficient detail. The model also predicts that closing (i.e. sealing) the individual bays of an engine can result in (nearly) zero CPMEP. This was confirmed by motored single cylinder engine measurements.