Lean Burn Combustion Influence on Stratified Charge Ethanol Direct Injection Engine

Direct inject engine provides increased possibilities to work with injection strategies in order to achieve better efficiency. Some ethanol properties such as the higher octane number, the latent heat of vaporization as well as the faster laminar speed made ethanol one of the most promising biofuels. These properties help to achieve knock suppression in a SI engine and therefore allow the use of higher volumetric compression ratio, which is one of the key factors in efficiency improvement. Several studies have showed ethanol as a way to reduce soot formation in direct injection engines as the oxygen molecule reduces the locally fuel-rich region. The use of ethanol contributes significantly to the reduction of total hydrocarbon (THC) and carbon monoxide (CO). On the other hand, the ethanol lower air-fuel ratio and lower heat value (LHV) in comparison to gasoline represents a significant disadvantage, since it increases the brake specific fuel consumption (BSFC) and CO2 specific emissions. This work conducted an experimental investigation of lean burn stratified ethanol direct injection. The tests were performed on a wall-guided optical single cylinder research engine at 1000 RPM for the lambdas of 1.00, 1.10, 1.20 and 1.30. The main flame development characteristics were studied from images obtained by means of shooting the combustion process. The authors believe the results founded in this work are useful in further develop ethanol direct injection strategies.