F1 tech for future Hondas: Prechamber combustion to maximise fuel efficiency
Honda are looking to Formula 1 car racing to address the demand for ever-cleaner engines – with a patent revealing a superbike engine featuring the sort of prechamber combustion that’s universal in F1.
While the turbocharged, hybrid V6 in those racing cars might seem a far cry from bike engines, the demands for efficiency, power and high revs mean there are clear parallels.
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The concept splits the combustion chamber into two areas. On each intake stroke the main section gets filled with a very lean fuel/air mixture, while the much smaller prechamber – where the spark plug sits – gets a richer mixture.
The idea is that the plug can easily ignite the rich mixture in the prechamber, which then allows jets of flame into the main chamber to make sure the lean mixture there burns efficiently without suffering the consequences of poor combustion, such as knock, or pinking.
In F1, prechamber combustion is combined with direct fuel injection and the rules only allow a single injector for each cylinder. Honda’s bike engine design isn’t hampered by these rules, so it uses a system of dual injection. That means it has one indirect injector, firing into the intake port as on most modern bikes, and one that adds fuel into the prechamber to achieve the richer local mixture.
Dual injection and prechamber combustion are well established (Honda used a version of the idea back in the 1970s on the original Civic, with a separate 'rich' carburettor), but Honda’s design gets clever in the way it separates the prechamber from the main combustion chamber. The chamber itself is largely made up of a rotary valve, driven from the camchain. It’s basically a rotating enclosure with cut-outs in its walls so as it turns it either isolates the prechamber or opens it to the main combustion chamber.
It connects the two chambers during the exhaust and intake strokes, ensuring all the spent gasses are replaced with a fresh charge, then separates the prechamber to allow its direct injector to add more fuel to that area.
When the plug ignites the fuel, the valve turns to expose an array of holes so focused jets of flame are directed into the main combustion chamber to make sure the lean air-fuel mix burns as completely as possible. The result? Maximum power and efficiency with low emissions. When Euro6 rules come into play, this is the sort of tech firms may well adopt to keep on top of the regulations without sacrificing performance.
The process in detail:
Into position Gears take drive from the intake camshaft to the rotating enclosure to move it and ensure it’s always in the right position. On the Fireblade-style inline four-cylinder engine in Honda’s patent a single shaft carries the rotating enclosures for all the cylinders.
Open and shut Rotating enclosure forms the main section of the prechamber and can separate the direct injector and spark plug from the main combustion chamber.
Keeps on spinning During the compression stroke the enclosure rotates to separate the prechamber from the main chamber and opens a small port to let the direct injector add more fuel to the mixture inside it.
Feel the burn At the point of combustion the enclosure exposes its wide opening to the spark plug and multiple small holes to the main chamber and sends jets of flame to ignite the leaner fuel/air mix.
Breathe out On the exhaust and intake strokes, the rotating enclosure exposes a wide opening to clear exhaust gas and refill with fresh mixture