The current generation of 6-liter turbocharged F1 V1.6 engines is undoubtedly the most advanced internal combustion engine ever developed. Only four manufacturers have taken the plunge and dared to make the heavy investment necessary to create them and, although Honda is withdrawing from the category after 2021, the engine manufacturer is already looking to transfer the technology developed in competition to production vehicles.
Although one would imagine that motor vehicles would be the beneficiaries, in many respects motorcycle engines are subject to high revs and high specific power similar to those of F1, and at least l ne of the key technologies of the latest era of F1 is set to be brought to production motorcycles in the near future.
The technology in question is called pre-chamber ignition and allows engines to use leaner mixtures and higher compression ratios, giving more power while consuming less fuel.
Getting the right mixture of air and fuel in an engine is one of the biggest challenges in maximizing performance. In theory, there is an ideal stoichiometric ratio between air and fuel (combustion can only occur when 1 g of gasoline is in the presence of 14,7 g of air), but engines generally run higher richer than this at high load (i.e. with more fuel) to decrease cylinder temperatures and reduce the risk of knock that occurs when the mixture in the combustion chamber self-ignites instead of burn in a controlled manner. The explosion caused by the knock can go as far as burning a hole in a piston in the worst case.
Pre-chamber combustion, as used on all current F1 engines, is a solution that allows the spark plug to ignite a very small pocket of rich mixture, with more fuel, then brings in the fuel jets. this burning mixture into the main section of the combustion chamber – filled with a much leaner mixture – to ignite it without causing a knock. The result is a more powerful, cleaner and more economical (but much more technological) engine.
In F1, the issue of prechamber combustion is complicated by rules that only allow designers to use one fuel injector per cylinder, making it difficult to have the required rich mixture in the prechamber and the lean mixture in the main combustion chamber. Not having these kinds of constraints on a production motorcycle, Honda designed a system – revealed in new patent applications – that uses two injectors per cylinder.
The first injector is completely conventional, sending fuel into the intake air just past the air intake throttle, so it enters the cylinder through the intake valve, as on any engine motorcycle that we know. The trick comes from the fact that there is also a second injector installed in a small pre-chamber, above the main combustion chamber. The spark plug also emerges into the pre-chamber and a rotating barrel driven by the camshaft selectively separates the pre-chamber from the main combustion chamber.
This is where Honda's patented motorcycle engine design is very different from F1 technology. The rotating barrel is a kind of tube with carefully positioned holes drilled into it, so that it performs several operations at different stages of the engine cycle as it rotates.
The main part of the barrel, which effectively forms the upper central section of the main combustion chamber, has a large port on one side. It is presented to the combustion chamber during the exhaust and intake stages – allowing the pre-chamber to be cleared of exhaust gases and filled with fresh (but lean) mixture.
During the compression phase, the barrel rotates to present a closed section to the main combustion chamber, while a small hole near the prechamber injector opens to introduce an additional jet of fuel into it.
At the time of ignition, the large port is located at the top of the barrel and a set of small ports align with the top of the main combustion chamber. When the spark plug ignites a spark, it ignites the rich mixture in the pre-chamber, and this ignited, expanding mixture shoots out in jets through the small orifices – spreading through the lean mixture inside the pre-chamber. main combustion to ignite it in a controlled manner. This is called torch lighting.
While F1 has recently focused its development on pre-chamber combustion, Honda's consideration of the same thought goes back much further. Indeed, Soichiro Honda had himself supervised the development of the Japanese company's "CVCC" (Compound Vortex Controlled Combustion) system in the early 1970s. This system fitted Honda Civics in the 1970s. Although he used a carburetor instead of injection, the CVCC featured a pre-chamber, where the spark plug was installed, and a second small intake valve which allowed a richer mixture in the pre-chamber than the mixture which entered the main combustion chamber.
This system allowed Honda to meet the 1975 US emissions limits without using a costly, heavy and power-reducing exhaust catalyst, while all its competitors had to adopt it.
Although the company's new patent application doesn't specifically indicate which motorcycles it might be aimed at, the illustrations clearly show the outlines of the FireBlade, suggesting that this system should be reserved for Superbike-style machines.
