Motoring Weekly recently published an article about Toyota upsizing their highly efficient engine, and late last year, Mazda applied for a new patent relating to their version of a revised internal combustion engine. They have called it the Homogeneous Charge Compression Ignition engine. Today they sell Skyactiv-G engines and this new one is dubbed Skyactiv-X.
It takes concepts found in diesel engines and applies them to a petrol motor and then takes those ideas further. At low revs the engine doesn’t use the spark plugs to ignite the fuel mix, instead it uses compression to create the power stroke. At the higher revs, the spark plugs are used to ignite the fuel. What this does is to create a very lean burn motor that provides a huge 20-30% increase in fuel efficiency.
This is rather like the idea for variable valve timing in that at low revs, i.e. town driving, the car will deliver great fuel economy yet when the driver wants to play, the engine is capable of switching to a higher power mode that uses more fuel. The engine is fitted with two standard exhaust driven turbochargers and an electric supercharger to be used whilst the turbos get up to speed, in effect flattening the linearity of the power delivery. They also added a little trick to get the turbos accelerating quicker – under 1600 rpm they use a valve in the exhaust system that narrows the pipe causing the gas pressure to rise. This in turn means that the gas travels faster towards the turbo vanes ultimately making them spin faster!
Media reports have suggested that Mazda will use an energy recovery system to power the supercharger – they have one called “i-eloop”. This system is a typical KERS unit that takes energy from the braking system and converts it to electricity and stores it in a capacitor, to be fed back into the car’s systems as needed and in this case it could be used by the supercharger.
It is interesting that Mazda and other manufacturers are still developing the internal combustion engines when Governments (today) are smarting over their focus on diesels and putting all their eggs into the electric basket. I think things will change and Governments will quietly drop (or delay) their bans on petrol and diesel because they were ill thought out. Mazda has the right idea, use new technologies to make the vehicles more efficient yet give them the power when needed.
The market needs a range of different power sources and Mazda are certainly generating new ideas to provide the choice.