Experimental Investigation of a Methanol Fueled SI Engine at Full Load Using a Central Composite Design

The large difference in fuel properties between methanol and gasoline demand the development of a dedicated spark ignition (SI) engine in order to exploit methanol’s properties for maximum thermal efficiency, rather than using the flex-fuel engines of today. In order to develop such an engine, proven technologies on a high efficiency gasoline engine are a good reference point to start with. The engine setup used in this work was a 1.6l turbocharged direct injection engine equipped with variable valve timing (VVT) and a low pressure EGR loop. A central composite design (CCD) was used to quantify the influence of five control parameters on the brake thermal efficiency (BTE) and main energy losses when running the engine on methanol at full load and a fixed engine speed of 1700 rpm. The set of control parameters consisted of the intake valve opening timing, exhaust valve opening timing, opening of the waste gate, opening of the EGR valve and opening of the backpressure valve. The main energy losses studied include the heat transfer loss, the frictional losses, incomplete combustion and exhaust losses. A prediction model was set up for each individual loss term and the results were compared to a prediction model of the BTE. While the loss terms were mostly influenced by the primary effects of the control parameters, the effect of them on BTE was shown to be minor and the influence of the interaction terms proved to be more significant here. The point of highest BTE was found to be at a BMEP of 22.5 bar with a value of 42%. These results can be used as an initial guideline for further optimization work where with the addition of a simulation model the mechanical limitations of an engine test bench can be overcome.