Discussion and questions related to the course Practical Diesel Tuning
I just finished the courses "Diesel Tuning Fundamentals" and "Practical Diesel Tuning".
In these courses the term 50% burn is used when talking about the combustion process. Can someone elaborate on this? How is this 50% calculated and how do you know if you are hitting this or not?
What I understood from Andre's lecture, there are two temperature spikes inside the combustion chamber, during a power stroke. The second peak occurs about 50% halfway through the combustion cycle. Lest having a manufactures laboratory to test in-cylinder temps, there's no way to measuring this point in the engine cycle. Two workarounds are applicable in this case, you can use the timing calculator (less precise), or do a timing sweep on a dyno (more precise). Out on the street though, in case you don't have a dyno, you'd rely on an indirect assessment via exhaust gas temperature.
Hope this helps
There is a special term in engineering - 50 percent fuel mass burn. It is specific figure that represents fuel burn rate property. Fuel does not burn equally - the first half burns kinda slowly whilst the second one burns very quickly.
This 50% burn is not something I know from the diesel industry. Sound more or less someone came up with it thinking it was I good idea as in reality looking @ real data form thermal en pressure sensor in the combustion chamber you can peak this second thermal spike a lot sooner depending on the what we call burn delay of diesel fuel that all depends on fuel pressure and quality of injection shooting NOX sky hi great for fuel efficiency and massive engine torque if the fuel system is able to produce large volume of injection in a short possible time.
Do think on meeting emissions 50% burn if no exhaust SCR is used could be close however if SCR and no EGR is used NOX pre SCR will be less of a problem making it possible to peak a bit more on combustion pressure a bit sooner giving better engine performance in general.
Without all the complicated sensors for combustion monitoring. Make some dyno pulls take out all pilot injection from about 200Kpa onwards manifold pressure to reduce injector dead time and use the first thermal spike or pre combustion to get some burn delay going as short after the second thermal spike or main combustion will progress a lot faster maintaining hi combustion pressure a lot longer. The only tricky part is the CR of your engine and how tolerant it will be on advancing start of injection on your engine.
Take in mind there is no book on how to do diesel stuff. It’s to many things that make the difference and not a lot of info is out there on how diesel systems actually work so as an outsider trail and error is needed to make progress so keep an open mind on things and discover.