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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.

The numerous variable valve actuation mechanisms for poppet valves need to be classified, if sensible comparisons are to be made, and one possible taxonomy is presented here. Not all the mechanisms proposed have been tested, but where they have it is usually with gasoline engines. It is well established that controlling the valve events can raise and flatten the torque curve. However, it is difficult to quantify and compare the gains in torque and consequential reduction in fuel consumption, as the results depend very much on the starting point. This is also the case when variable valve actuation is used to reduce engine emissions. Fortunately it is quite easy to realise suitable variable valve timing systems for controlling the valve overlap, and the point of inlet valve closure. The other main application to gasoline engines, is in obtaining load control without throttling.