The buzz around the Formula 1 paddock about the heavily upgraded Renault engine set to debut in Canada is that it will feature the same trick combustion technology that is already believed to be employed by Mercedes, Ferrari and Honda. Homogenous Charge Compression Ignition (HCCI) combines diesel-like compression ignition within a petrol-fired engine. But the latest F1 engines have not forsaken spark plugs. Rather they use a combination of compression (spontaneous) ignition with conventional spark-fired ignition, depending upon operating loads.

It is believed the dome of each piston has an extension in its centre, fitting into a recess within the combustion chamber. Within this ‘chamber within a chamber’ the mixture is compressed to the point of spontaneous ignition, but the main lower chamber features a spark plug for conventional spark-led ignition. It brings significant efficiency gains, allowing the knock limit to be considerably extended. When in compression ignition mode, the ignited mixture in the small chamber ignites the mix in the bigger chamber as the piston falls. It means that only the mixture in the small chamber needs to be rich, allowing that in the lower chamber to be relatively weak. It gives greater power for the same fuel consumption or less fuel consumption for the same power. When in conventional spark plug mode either the upper chamber is not fed with fuel or the extension in the piston is a ‘plunger’ type that can be extended or withdrawn.

HCCI engines have been heavily researched by the road car industry – notably by GM, Mercedes and VW. They promise not only a better fuel economy/performance trade off but also much lower NOx emissions, because the higher temperatures created by the compression ignition produces less soot. But there has so far been no production engine using this technology. Controlling the spontaneous burn has proved extremely difficult.

But in combining the HCCI principle with part-time spark plug ignition, F1 has apparently perfected a hybrid version. A pure auto-ignition engine has a small power band – controlled at low revs by knock and at high revs by combustion chamber pressures. But perfecting the software to allow the advantages of HCCI principal at appropriate revs and loads, but switching to conventional ignition outside of those limits has proved feasible. The characteristic ‘misfire’ sound of the Honda on part throttle is believed to be the audible giveaway of the changeover point between the two modes.

The effect can also be heard – but less aggressively – on the Ferrari. With the Mercedes however, there is no aural evidence. It’s believed the Mercedes engine has featured this technology from the start in 2014, that it was also incorporated into Honda’s first engine last year and that Ferrari adopted the technology last year. Renault would this be the last of the four manufacturers to introduce it. Although details are sketchy at this point, it’s clear that this new technology has been a major part of the F1 power war in the hybrid turbo formula.

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