DISI and Duty Cycle

[shaodome]

OK, so I haven't seen much on the forum about it yet from the posts I've read, so I figured I would start one. If I missed it, please hook me up with a link.

I've read some things about our stock injectors not being anywhere near maxed out and the cam pump being a limitation, while I am not disputing the cam pump (aka look at laloosh, nice work btw man!), I am not so sure about the injector duty cycle headroom being as high (seem claims of 600hp) as some are stating.

With direct injection, it seems the injection event has to occur at a very precise point when the piston is at the peak (or near that) of its compression stroke. Now, with a port injection engine, you have a significantly bigger window available to inject fuel, thus there is room to increase the PW of the injector as opposed to the amount of flow at the stock PWs (within reason).

Does anybody have any more technical information with regards to direct injection? What about the diesel guys? What do they do?

 

[dadasracecar]

I datalogged my last dyno run and the injector duty cycle was at 31%. That valued should be doubled for a DI engine for reasons you've already mentioned. THat puts us at ~62%.

 

[shaodome]

Good to know, but where did you come up with the "doubled" value? Is that an assumption based on your experience or some other factual source? SAE papers, etc? Thanks in advance.

 

[dadasracecar]

I got it from Jordan at CP-E. He's an engineer there and I think he has a degree in mechanical engineering with an automobile emphasis or automotive engineering or something. It's not what you want, but if he says it, I trust it. You could probably call cp-e and talk to him.

 

[mrlilguy157]

I'd like to see some writeup or documentation. I'll make some calls tomorrow if I have time.

 

[shaodome]

I got it from Jordan at CP-E. He's an engineer there and I think he has a degree in mechanical engineering with an automobile emphasis or automotive engineering or something. It's not what you want, but if he says it, I trust it. You could probably call cp-e and talk to him.

I've been meaning to talk to Jordan (heh..I'm a Jordan as well) about the future CP-e stuff, but I haven't had a chance and didn't want to take up his time until I was a paying customer (waiting on throttle control). Guess I'll give him a call....

It doesn't matter to me if the sources has a degree in cooking or not, just where the information is derived with a logical explanation.

 

[Rotus8]

Think about the engine a little. It is a four-stroke. Two of the strokes are power and exhaust, you don't want to be squirting fuel in during that time, it just goes out the exhaust valve. That leaves intake and compression. You probably don't want to be squirting at the very beginning of the intake stroke because the exhaust valve is still open a bit. You don't want to be squirting after the plug fires, which is a bit before the top of the compression stroke. This leaves only about 45% of the time you can have the injectors open.

 

[shaodome]

Again...from my understanding of direct injection is that the primary fuel squirt enters the cylinder at near peak compression, if not TDC. So since you have that VERY small window it would seem like you would have even less time than the 45% DC limit.

Interesting discussion and pretty cool technology