Experimental studies on the effect of injection timing in a SI engine using dual injection of n-butanol and gasoline in the intake port

Alcohols can be used in spark ignition (SI) engines along with gasoline in the blended form. However, phase separation which occurs in the presence of moisture restricts the amount of alcohol that can be blended. On the other hand, for effective engine operation, the ratio of alcohol to gasoline has to be varied based on the engine operating condition. n-Butanol has properties close to gasoline and has not been widely investigated as an engine fuel. In this work, two injectors were mounted in the intake port of an automotive SI engine (bore = 62 mm, stroke = 66 mm, compression ratio = 9.4) to inject gasoline and n-butanol separately so that the fuels hit the back of the intake valve. The engine was fully instrumented for the measurement of performance, emissions and combustion parameters. Initially experiments were conducted with simultaneous injection of n-butanol and gasoline (1:1 mass ratio = But 50S) using the two injectors with different injection timings at 25% and 60% throttle positions at 3000 rpm. Subsequently different injection timings for the two fuels were tried to study the influence of sequencing. The results were compared with gasoline and n-butanol (But100) using a single injector. Around 26% reduction in hydrocarbon (HC) emission with simultaneous injection of gasoline and n-butanol (But50S) at 25% and 60% throttle positions was observed with an injection timing of 64° CA before in let valve opening as compared to open valve injection. B100 was superior at high throttle positions and gasoline or B50S was suitable at 25% throttle as regards performance and emissions. At 60% throttle, injecting n-butanol just before the start of injection of gasoline is beneficial for reducing HC and carbon monoxide (CO) emissions. In the case of lean operation (equivalence ratio of 0.82) there is no significant influence of injection phasing except for a small improvement in thermal efficiency. On the whole this method of operating the engine can lead to good engine performance over wide operating conditions since the ratio of the fuels can be varied.