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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. [ABSTRACT FROM PUBLISHER]

This paper describes a simple, analytical, control-oriented and physically-based model for prediction of combustion timing during PCCI combustion. The model includes direct dependence on in-cylinder temperature, in-cylinder pressure, and the total in-cylinder O2 mass fraction. It is extensively validated with experimental PCCI data from a multi-cylinder engine with almost exclusively stock hardware (stock pistons, injectors/nozzles, turbocharger, etc.) and variable valve actuation. The results show that across a wide range of input conditions the model predicts the start of combustion (SOC) within ±2°CA of the experimental values for all but one of the 119 data points. The experimental SOC ranges from as early as 19.3°CA to as late as +0.6°CA by heavily exercising the control authority over SOC provided by SOIecm, IVC/ECR modulation (ECR ranges from 12:1 to 18:1), and the engine's air-handling system. This PCCI combustion timing model can be coupled with a gas exchange model for control algorithm design. [ABSTRACT FROM PUBLISHER]

Advanced diesel engine architectures employing flexible valve trains enable emissions reductions and fuel economy improvements through advanced combustion strategies. These combustion strategies, such as pre-mixed charge compression ignition (PCCI), homogenous charge compression ignition (HCCI) and low temperature combustion (LTC), are controlled and enabled through the use of flexible valve trains. The in-cylinder oxygen concentration serves as a critical input in controlling these strategies. Unfortunately, the in-cylinder oxygen concentration is extremely difficult to measure on production engines. However, the oxygen concentrations in the intake and exhaust manifold can be utilized to calculate the in-cylinder oxygen concentration when the charge and residual in-cylinder mass are available. A model-based observer is developed to estimate the oxygen concentration in the intake and exhaust manifolds. The oxygen concentration estimates will be sensitive to errors in the mass flows of the manifold filling dynamics. To improve the EGR flow measurement, a high-gain observer is implemented to provide a more accurate EGR flow estimate. The observer estimates the oxygen concentrations to within 0.5% O2 and converges in less than 0.5 seconds. [ABSTRACT FROM PUBLISHER]