This is how the combustion engine is being reinvented

Many players and technologies are emerging in the automotive industry with the aim of ‘banishing’ internal combustion engines, but some manufacturers, such as Bosch and Mahle among others, may be working on a revolutionary combustion engine.

Mahle, the German company behind many engine design innovations over the past 100 years, has developed a combustion system called Mahle Jet Ignition (MJI). It is already in use in the engines of a major Formula 1 team and will also be part of a new modular hybrid propulsion system that should make it easier to produce petrol-electric hybrids.

The MJI system works as follows. In a traditional petrol engine, fuel is injected into the intake ports along with the incoming air (indirect injection) or directly into the combustion chamber (direct injection). The new MJI technology comes in two types: active and passive. The first incorporates both types of injection. The port injector works in the normal way, but the tips of the direct injector and the spark plug are placed in a small pre-chamber immediately above the main combustion chamber.

During the intake cycle, the port injector sends 95% of the fuel into the intake port, which rushes into the main combustion chamber and is then compressed by the piston as usual. As this happens, the remaining 5% is injected into the pre-chamber and ignited by the spark.

https://www.youtube.com/watch?v=n6Eutw0WU3U

This is how Mahle’s new MJI system works

As it ignites, the partially burned jets of hot fuel and air are forced through small holes in the bottom of the pre-chamber, igniting the main charge as a whole rather than at a single point near the spark plug. Combustion is faster and more uniform, with faster pressure build-up to generate power more quickly. The whole process is homogeneous (fuel and air evenly mixed) and can run ultra-lean (a much higher air-to-fuel ratio) when less power is needed.

The latest ‘passive’ version (used in F1) removes the direct injector, with just a spark plug in the pre-chamber. It is not a new idea: Honda developed the compound vortex-controlled combustion chamber for its first-generation Honda Civic in the early 1970s, but its execution was more complicated than Mahle’s passive MJI.

As the fuel and air mixture is drawn through the intake ports into the combustion chamber and compressed, a small amount of the main charge is pushed through the nozzles into the pre-chamber. There, it is ignited by the spark plug, and the high-pressure jets of burning fuel and air are forced back out through the nozzles into the main charge, igniting it as before.

Higher compression ratios than normal can be used before knock (pinking) becomes a threat, which further improves fuel efficiency. Exhaust gas recirculation and cool air during lean combustion reduce combustion temperatures and significantly reduce NOx by 99% in the ultra-lean area of the engine’s operating range. Hydrocarbon emission levels are equivalent to those produced by a normal port-injected petrol engine, and particulate levels sit somewhere between port and direct injection.

Both versions of MJI can be applied to virtually any petrol engine and can operate across the entire operating range of the engine. With that in mind, Mahle is in advanced talks with several car manufacturers, so watch this space.

Also suitable for hybrid vehicles

Mahle has also announced a modular hybrid powertrain (MHP) that uses the ‘passive’ Mahle Jet ignition in its petrol engine and should provide a practically turnkey powertrain solution for vehicle manufacturers. It can be configured with a turbocharged two- or three-cylinder engine and a one-, two- or four-speed transmission. Because of this, the MHP can be scaled to fit anything from a segment B car to a larger segment J SUV.