They've turned everything upside down and inside out with this engine.
It is an unthrottled petrol engine, meaning it takes a full gulp of air for each cycle, no matter how much petrol is burnt. Conventional petrol engines have the fuel/air mix carefully matched (stoichiometric mixture).
It has a compression ratio (CR) of 18:1. The previous maximum was 14:1.
The fuel is injected directly into the cylinder when the piston is at the bottom of the cycle. For Compression Ignition (CI) engines, it's usually around the top of the cycle.
There is no spark plug.
The fuel is perfectly mixed with the air (homogenised) on the up stroke. Because there is much more air than required to burn all the fuel, it is a very lean (weak) mixture. When the piston gets to the top, the heat of compression causes the whole mixture to react instantaneously. There is no flame front burning through the mixture as with a spark engine, or a flame front on the drops of fuel from a conventional CI, because there is no spark or drop of fuel. It's these flame fronts which are very hot, and create the NOX. There are no drops of fuel to provide soot particles either, the scourge of Diesel engines. The whole mixture burns so cool that soot and NOX aren't formed. And because the combustion is instantaneous throughout the mix at precisely the right point for maximum power you literally get the best bang for your buck, leading to an economy figure of 3.3l/100km.
