Effective compression ratio estimation in engines with flexible intake valve actuation

The ability to modulate the effective compression ratio (ECR) of an engine is a key enabler of advanced combustion strategies. ECR is a measure of the effective in-cylinder compression of gases above intake manifold conditions. An engine´s ECR is usually computed from in-cylinder pressure data, requiring reliable in-cylinder pressure sensors that are not typically found on production engines. As such, a method is needed for determining the effective compression ratio using only information available from stock engine sensors, including manifold pressures and temperatures and air flows. The work outlined here presents a strategy for estimating the ECR without need for in-cylinder pressure data. The estimation scheme was transiently tested and compared to experimental engine data from a unique diesel engine test bed with flexible intake valve actuation, and was able to converge within 3 engine cycles after a transient event with less than 6% average steady-state error compared to experimental engine data.