Gasoline Engine Operation with Twin Mechanical Variable Lift (TMVL) Valvetrain Stage 1: SI and CAI Combustion with Port Fuel Injection 2005-01-0752

This paper describes the results of the first stage of an integrated experimental and modelling programme on a gasoline engine with Twin Mechanical Variable Lift (TMVL) capability.

The engine used for this work was a modified version of a 4 cylinder, 2.0 litre BMW engine. The modified engine has the “Valvetronic” continuously variable lift valvetrain on both the inlet and exhaust valves and dual independent cam phasers with 60 crankshaft degrees of phasing authority. The Valvetronic system allows continuous variation of the valve lift from a minimum of 0.25 mm to a maximum of 9.7 mm.

Three operating modes were investigated with port fuel injection:

• Conventional throttling with dual cam phasers - spark ignition combustion
• Inlet valve throttling with dual cam phasers - spark ignition combustion
• Inlet valve throttling with Controlled Auto Ignition (CAI) combustion

For the spark ignition cases, a Design-of-Experiments (DoE) approach using in-house Stochastic Process Modelling (SPM) and optimiser tools was used to optimise the control variables for best fuel economy and to gain an understanding of the trade-offs between economy, emissions and combustion stability. Inlet, exhaust and cylinder pressure data was recorded from all 4 cylinders for combustion and pumping work analysis.

In parallel to the experimental programme, a 1-D gas dynamic simulation was carried out using the Ricardo WAVE code. The model was validated using the measured cylinder, inlet and exhaust system instantaneous pressures. The model was used to derive in-cylinder conditions at the experimental test points.

The paper contains a description of the engine and the test and modelling methods. Part load fuel consumption, emissions and combustion characteristics are compared for the three operating modes investigated. The advantages of valve throttling and CAI combustion are quantified.