Homogeneously charged compressed ignition one could translate it. Without going too deep into a description of this, it is based on the injection of hydrogen taking place as we described in the PFI system, i.e. in the inlet port right next to the inlet valve but on the outside of the combustion chamber. They use a homogeneous mixture of air and hydrogen, which is also very lean. This mixture is injected directly into the combustion chamber and due to its flammability it is ignited by the high compression and then ignites the supplied hydrogen. What has proven to be a great advantage of this system is that NOx has been reduced to really low figures as a residual product in the exhaust gasses. This, moreover, with maintained power from the engine. NOx is close to zero. But even this system needs further development to function, among other things very high compression is required to name a few.[1]


[1] Ibid. s. 7