Investigation of advanced valve timing strategies for efficient spark ignition ethanol operation

Biofuels for internal combustion engines have been explored worldwide to reduce fossil fuel usage and mitigate greenhouse gas emissions. Additionally, increased spark ignition (SI) engine part load efficiency has been demanded by recent emission legislation for the same purposes. Considering theses aspects, this study investigates the use of non-conventional valve timing strategies in a 0.35 L four valve single cylinder test engine operating with anhydrous ethanol. The engine was equipped with a fully variable valve train system enabling independent valve timing and lift control. Conventional spark ignition operation with throttle load control (tSI) was tested as baseline. A second valve strategy using dethrottling via early intake valve closure (EIVC) was tested to access the possible pumping loss reduction. Two other strategies, negative valve overlap (NVO) and exhaust rebreathing (ER), were investigated as hot residual gas trapping strategies using EIVC as dethrottling technique. Several part load conditions were tested at 1500 rpm with stoichiometric ethanol port fuel injection during the intake stroke. Spark assisted compression ignition (SACI) was achieved with ER at some loads. The use of EIVC load control strategy was effective to reduce part load pumping losses. Both strategies with residual gas trapping provided increased indicated efficiency and considerable NOx emissions reduction.