He has a racing ECU, which do not care about pollution requirements. Diesel always inject what is demanded by torque and do not care about fuel to air mixture. This is only limited in cars through the injection mapping. The mixture is done by the injector which creates a swirling spray pattern, maximizing the surface area of the injected fuel. This mixture starts to burn then from the outside, aka flamefront. This is the reason that mixture ratio is nor of concern.