Engine technology developments are moving at a rapid pace! The main driver being ever more stringent emissions regulations, in combination with market expectations – no-one is going to buy a car with less performance due to emissions compliance! This is a tough challenge for any vehicle OEM but it is promoting an exciting breeding ground for the latest developments in engine and vehicle technology. So, what are these likely to be?...
Smaller engines with higher power outputs are already a fast moving trend (downsizing), this trend will continue - with almost unbelievable targets. Development goals of gasoline engines producing 200kW/litre are being considered by OEM's – the biggest challenge here being durability – that is, how to make such a powerful engine last in production. These gasoline engines could be classified into lower and higher power engine design catagories – with the break point between them being around 180kW/litre. For lower power densities, the main enabling technologies will be the adoption of Miller cycling and cooled EGR, in conjunction with cylinder deactivation and variable compression – although this latter technology is expensive!
|Figure 1 - Saab variable compression concept|
In addition, Miller cycling requires specific design attributes for the inlet air path, valves and combustion chamber – reason being, to promote strong tumble in the incoming charge as this ensures enough charge motion to provide good turbulence in the mixture, for rapid flame growth – that would otherwise be compromised due to the late closing of the inlet valve.
|Figure 2- Miller cycling|
New spark plug electrode designs are under development in order to produce turbulent jets of burning mixture into the combustion chamber, as opposed to just an electrical arc to provide an ignition source. Laser ignition has shown very promising results, however, at the moment this technology is still confined to the laboratory as it is expensive and physically too large for production applications.
|Figure 3 - Electric cylinder charging systems will become the norm.|
For higher power densities (likely to be adopted in performance vehicles) variable cylinder charging and porting concepts will be used in addition to the above developments. Multiple charging systems (turbo, super and e-booster) will be used to employ charging and evacuating of the cylinder. Dual injection systems will be used, with port injection for use at high-load conditions, to reduce particle emissions.
|Figure 4- Dual Injection systems to reduce PM emissions from gasoline engines|
For very high performance engines, in order to provide the required durability, it is likely that control system strategies will be used to ‘limit’ engine power below normal operating temperatures (cold start and running). This restriction will allow an increased safety margin for engine components - promoting longer engine life. In addition, these strategies could include the adoption of a ‘spark plug cleaning’ mode – to ensure that a high performance vehicle that is not driven with sufficient load/speed regularly, will not break down due to fouled spark plugs. (similar in concept to DPF regeneration).