Discussion and questions related to the course Diesel Tuning Fundamentals
We start building some what outdated semi truck race engines some years ago as customers want a low weight compact engine so logical step is to improve on things and that goes for the fuel system as well.
We also are involved in new engine development and load of this is done behind closed doors but we get most of the data as it will benefit the projects so we are able to compare this.
First question we had is it possible to upgrade older type injectors so we can get more fuel and accuracy out of them? Realty is the injector in use can hardly run @ 2100Bar fuel feed pressure and as most modern semi truck engines run @ 2400 to 2800Bar and have seen a fuel per stroke increase up to 33% so it will not be an easy job with a possible downside on things.
First step we took as build a nozzle with the latest injector specifications with marginal bigger holes as to what the standard nozzle has in use and due to the better flow characteristics and accuracy of the nozzle hole size we get more than 50% flow increase on the injector on a low interval test 1600Bar feed pressure so that more than 20% flow rate over the 100Bar flow test done on the nozzle it self. More about this later on.
What about accuracy? Well that’s the parts where we excel with perfect hole size and shape but nothing more than logic as we are using stuff that makes the injector parts for last generation engines with lower emissions so with this we are able to build injectors that flow more that are over 2,5% more accurate on flow numbers between them so if things will chance on flow rate in relation to injector control we have a chance all injector will do the same.
So what about injector control? Almost all Commonrail injector use a pressure balance to open and close the injector and on most injectors flow rate and balance are related so chance one of them and the other will react as well. So what was the outcome? On idle and low load fuel flow and electrical injector on time we seen a decrease on fuel but still consisted injector response time so what is going on? In short needle lift is less as pressure drop in the injector is bigger resulting in flow restriction. Whoops forgot to mention needle we use have multiple angels for different lift/flow rates but still if we use the same nozzle hole size as original we get more fuel out of them indicating the is a difference there.
So what happens on 75% load mid RPM simulation and what will be the outcome on changing needle travel? We use the 100Bar flow test to find out what will be the optimal injector needle lift as @ some point your not getting more flow from the nozzle so there is a sweet spot. So often the mistake is made to get more needle lift and as a result fuel flow shoots up but why? Due to a chance in pressure differential in the injector needle travel becomes slower so it also takes more time to actually close the injector and if you go to extremes it can add up to 3x what’s normal. So in all there is a fine balance between needle lift nozzle flow rate and injector internal working and as you can understand on last generation injector big steps are made to get that over 33% more flow rate working very accurate for a long time so yes we are able to get close with older type injector but not nearly as close a most think.
As for an easy injector upgrade if you get lucky look for newer models engines as chance is they will have bigger injector fitted as standard so you do not have the go the way for extruder honing your nozzle by some tuning shop often have to ask your self dos the flow increase come from nozzle hole size of needle lift or injector in balance?? As for smaller engines we where able to do an easy injector upgrade with some Duramax engines changing injector and fuel lines.
Also take in mind unless things are done in big numbers of production injector upgrades cost money as it will need loads of time and special equipment to do things the proper way so maybe needles to say we often get the same results with less fuel and smoke stepping back closer to original hardware used as for factory produced hardware is hard to beat.
thank you very good reading