This system is based on having direct injection DI and PFI. The direct injection is for giving a so-called "pilot injection", this means that you inject a small amount of diesel directly into the combustion chamber. The diesel is ignited by the heat of compression and when hydrogen is later injected into this it is ignited. But even this system comes with certain disadvantages such as unwanted self-ignition. The NOx content is also too high for this method to be classified as zero emission, but further studies are being carried out in the laboratories. But despite the fact that PFI systems are relatively easy to convert to hydrogen operation, perhaps they should be seen more as a transition from our usual fossil-burning engines to more advanced engines that are hopefully not too far off in the future.[1]


[1] Ibid. s. 8