Injector technology for GDI racing engines

[riff_raff]

Current injection technology isn't fast enough to create layered charges by multiple injection events...

WhiteBlue,

Actually, modern direct-acting piezo injectors can achieve very high frequencies (ie. single injection events of .10ms or less). In production diesels, it is now common to have up to 5 discrete (pre/main/post) injections per cycle with a 5000 rpm engine. GDI injectors tend to use much longer injector PW's due to the much lower rail pressures used and the larger mass of fuel that must be delivered per injection.

GDI injectors could go to higher rail pressures in order to improve spray atomization and reduce injection PW. But accurate control of fuel mass delivery becomes problematic with higher rail pressures. Gasoline engines must operate over a fairly narrow range of equivalence ratios, and thus require precise metering of fuel based on measured intake air mass flow. Diesel engines are insensitive to equivalence ratio, so super-accurate fuel metering is not so critical and extremely high (2000 bar) rail pressures can safely be used.

Regards,
riff_raff

[WhiteBlue]

@ riff_raff

Your information is well known. In this thread we commented on the HDEV4 piezo operated outward opening petrol injector by Bosch which operates at 200 bar. The reason it can't be used for stratified injection is the high rotation speed of petrol performance engines and the problem of suppression of spontaneous self ignition (knocking or pinging).

Racing diesels, as you mentioned, run 5,500 rpm while commercial HP petrol engines with direct injection like the Ferrari 458 run 9,000 rpm. This is much exceeded by racing engines with port injection that can run 21,000 rpm as we all know. The problem is further compounded by the lubrication aspects of the fuel. Diesel oil has reasonable lubrifying properties for diesel pumps but petrol is a poor lubricant. The development of petrol fuel pumps for pressures exceeding 200 bar is not a simple issue, nor is speeding up the piezo injectors.

Finally the injection technology of choice is spray guided injection which is restricted to a very narrow window of the compression stroke between 30° and 20° in order to produce an ignitable mixture at the spark plug. Spray guided injection by nature produces a stratified charge but the required geometries of injector and spark plug are restrictive to multiple injection events.

If I speculate a solution to a higher rpm stratification range could be multiple injectors and accumulator rail supply at higher pressures exceeding 200 bar. Actually this field of research is very young and I am by far no expert there. I have just read two books that deal with the issue, but it is a fascinating technology.

[WhiteBlue]

Perhaps we can revive this old thread and add more recent knowledge.
https://www.highpowermedia.com/blog/3359/directly-so An introduction to combustion methods