AEC researchers have helped to develop an advanced spray-guided direct injection engine, which delivers significantly increased fuel efficiency while minimising emissions. Researchers from the Centre of Automotive Engineering collaborated successfully with Ricardo UK and PETRONAS, the Malaysian technology and energy company.
The research team focused on investigating the fundamentals of gasoline combustion using advanced analysis methods and laser diagnostic tools. Using optically accessed research engines located in the Sir Harry Ricardo Laboratories based at the university, researchers have been allowed unprecedented views into cylinders in order to analyse induction, fuel injection and combustion, validate simulations and optimise design.
The initial part of the programme enabled the successful development of a next-generation stratified charge combustion system based on spray-guided fuel injection (SGDI) with up to five injections per cycle. Subsequent research work on the multi-cylinder turbo-charged SGDI (T-SGDI) research engine has demonstrated that fuel consumption benefits were significantly enhanced through boosting, with a best brake specific fuel consumption (BSFC) of 203 grams per kilowatt hour (g/kWh) being achieved at 2250 revolutions per minute (rev/min) and 13 bar brake mean effective pressures (BMEP).
Further research led to insights that enabled the broadening of the stable combustion range for unthrottled, stratified operation of the ‘third- generation’ spray guided direct injection (SGDI) engine, incorporating piezoelectric fuel injectors, variable valve actuation (VVA) and advanced ignition systems.
Multiple fuel injection strategies were used to increase the unthrottled operating range, leading to further improvements in fuel economy. However, careful optimisation of these strategies is essential to ensure that benefits are maintained while further minimising emissions within combustion stability limits and consumer driveability demands.
One of the key aspects of the T-SGDI combustion system is the use of a multiple injection strategy. Whereas this approach is used effectively in modern diesels to control combustion rate, the T-SGDI combustion system uses multiple injections to limit spray penetration and hence avoid wall wetting. If optimised appropriately across a wide range of operating conditions, as in the T-SGDI system, the approach allows a stoichiometric mix to be focused in the region of the spark plug immediately prior to ignition. In addition to enabling fuel economy benefits to approach the theoretical optimum through unthrottled operation, the concept also offers enhanced exhaust gas recirculation (EGR) tolerance and is inherently low in nitric oxide and nitrogen dioxide (NOx).