Multidimensional CFD Studies of Oil Drawdown in an i-4 Engine

A computational study based on unsteady Reynolds-Averaged-Navier-Stokes that resolves the gas-liquid interface was performed to examine the unsteady multiphase flow in a 4 cylinder Inline (i-4) engine. In this study, the rotating motion of the crankshaft and reciprocating motion of the pistons were accounted for to accurately predict the oil distribution in various parts of the engine. Three rotational speeds of the crankshaft have been examined: 1000, 2800, and 4000 rpm. Of particular interest is to examine the mechanisms governing the process of oil drawdown from the engine head into the case. The oil distributions in other parts of the engine have also been investigated to understand the overall crankcase breathing process. Results obtained show the drawdown of oil from the head into the case to be strongly dependent on the venting strategy for the foul air going out of the engine through the PCV system. Results also show the dynamic holdup of oil in the steady operation to be highest near the crankshaft and pistons. Results are presented to show how the rotational speed of the crankshaft affects the nature of multiphase flow inside the engine and its influence on the drawdown of oil from the head into the case. The computational study was validated by comparing the computed volume of oil in the sump in steady state operation with the experimental measurements. The computational strategy presented in this study to simulate the crankcase breathing process can be most useful in guiding the design and development of engines.