What is it?
No humble Vauxhall Vectra; this is a test mule for General Motors’ very latest petrol engine technology.
Called Homogenous Charge Compression Ignition (HCCI for short), this is a system that combines the latest variable valve timing and direct inject petrol technology with cylinder pressure sensors. They allow the engine to burn its fuel at a lower temperature and therefore more controllably and efficiently.
HCCI returns 15 per cent better fuel economy than a conventional petrol engine, and because it burns the fuel at lower pressure, it also produces no harmful nitrogen oxides. Clever.
What’s it like?
The simple (but rather boring) answer is exactly the same as a current petrol engine.
After an exclusive sample of a 2.2-litre Vectra fitted with HCCI tehnology, we’d say it has the same level of flexibility and the same accelerative power.
On this prototype there was a noticeable step when it was switching between normal and HCCI combustion (the car uses normal spark combustion under full throttle and above 55mph). However, that was the only way any difference between it and a standard Vectra was evident.