Reducing fuel consumption and emissions, and increasing the efficiency of an internal combustion engine, while retaining power and keeping costs in check, is a delicate and difficult balancing act. At the pinnacle of motorsports, Formula 1, engineers have employed prechamber combustion to achieve the levels of efficiency mandated by the rules, while still remaining competitive. Cycleworld.com recently reported on a new Honda patent that shows a CBR1000RR fitted with a prechamber combustion system with some unique twists.
Prechamber combustion allows an engine to operate with a relatively lean fuel/air mixture that a conventional engine would have issues with. A lean mixture is difficult to ignite, so conventional engines typically add more fuel to aid in combustion. The result is a decrease in efficiency (more fuel is used) and an increase in emissions (more unburnt fuel is expelled through the exhaust).
Prechamber combustion uses, you guessed it, a prechamber that collects a rich mixture of air and fuel that is easy to ignite, and the resulting combustion flame is shot into the main combustion chamber where a lean mixture is waiting to be ignited. This lean mixture would not be able to be ignited by a conventional spark plug, but the shot of flame from the prechamber is sufficient to light it.
Whereas F1 engines are restricted to a single injector per cylinder, the Honda patent is for a dual injector setup, with one injector in the prechamber, and one in the intake tract.
While typical prechamber systems use a series of holes between the prechamber and the main combustion chamber to produce an array of small flames shooting into the combustion chamber, the Honda patent outlines a unique valve arrangement between the two chambers. Essentially a rotating tube, the valve has three stages: open, closed, and a series of holes. The open stage allows a complete purge of burnt mixture from the prechamber. Closed allows the prechamber injector to fill the prechamber with fuel without any escaping into the main combustion chamber. The series of holes is exposed to allow the prechamber combustion to shoot an array of small flames into the main combustion chamber to ignite the lean mixture waiting there.
As usual, the existence of a patent does not ensure the technology will reach production, but with European emissions standards getting stricter with every generation, a prechamber combustion system, combined with dual injectors, would be one way to keep internal combustion engines feasible for the near future. Interestingly, Honda was one of the pioneers of prechamber combustion in the 1970s with their CVCC engines, designed to meet emissions standards without the use of a catalytic converter. Whether Honda will essentially return to its roots with a modern take on the system remains to be seen.
Sources: cycleworld.com, drivetribe.com