The GDI injector can begin injecting fuel as soon as the exhaust valve closes, and can continue injecting fuel until just before the spark plug fires. So the GDI injection duration could theoretically be something like 270 crank degrees or more (if needed). Though in practice, it is usually a much shorter duration.
On the other hand, since the DI diesel injection event controls both fuel delivery and ignition timing, the main fuel injection event must be carefully controlled to begin about 10 or 15 degrees BTDC, and must be fully completed within about 5 to 10 degrees ATDC. That's only about 25 crank degrees at most.
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
mx_tifosi wrote:Is DI expensive to apply in production engines?
Isuzu had a truck, the Axiom, that had a 3.5L DI V-6 that they were selling for less than 35K.... so i can be done... we will be seeing it more & more soon.
Actually, I believe Ferrari used direct injection on their F1 engine a few years ago. The benefit is that it helps with volumetric efficiency. The fuel mass flow comprises around 10% of the intake charge mass. If the fuel can be delivered directly into the cylinder and does not have to flow past the intake valve, then that would essentially allow 10% more air mass flow. All other things being equal, 10% more air mass flow will produce roughly 10% more power. That's pretty significant.
There are lots of production car engines currently using GDI.
Regards,
Terry
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
There was a question about the number of permitted fuel pumps. I don't know if there is a limit, but I know that Honda was running more than one fuel pump when they were accused of using fuel as ballast in 2005. If I remember correctly, at the time they were running three fuel pumps: an electric pump in the tank to feed into a small reservoir; an electric pump in that reservoir to feed the engine pump; and a mechanical pump on the engine to pressurize fuel for the fuel rail. I am not certain about the details, but I know for sure that at the time they used more than one.
Regarding GDI boosting fuel economy, I don't think it would help much in F1. Gasoline won't burn except in a very narrow mixture range. Normal port fuel injection achieves good fuel economy by running the engine as close to the lean limit as possible except when maximum power is needed. GDI can deliver better fuel economy because it can improve on this concept. GDI can run a mixture that is on average leaner than should normally be able to burn. It does this by delaying injection until just before the ignition event. When the injector injects, it injects into the air immediately surrounding the spark plug(s). This creates a rich pocket of air/fuel mixture immediately around the spark plug(s) that is suitable for combustion. The air outside of this rich pocket is largely devoid of fuel, and far too lean to burn. So, on average the mixture in the cylinder is too lean to burn, but because the injection can take place so late in the compression cycle, the air surrounding the spark plug can be perfect. Interestingly, there is no reason that injection has to occur entirely before ignition. GDI could allow a small amount of fuel to be injected before ignition and then inject the remaining fuel directly into the resulting fireball after ignition. This is pretty much how common-rail Diesels work, but I don't know if any current GDI engines do this.
The reason I don't think GDI would help F1 fuel economy much is because F1 engines spend most of their time on track at nearly full power. In this mode of operation, the ECU would try to optimize the fuel mixture for power and burn all of the air in the cylinder. Port fuel injection does that very well because there is a lot of time for the fuel to mix with the air. For GDI to do this well, it would have to begin injecting fuel pretty early in the intake cycle, which wouldn't really be much of an improvement over port fuel injection.
One way that GDI could help F1 fuel economy would be by increasing power. As noted by another poster, GDI allows the engine to breathe more air because the fuel does not flow past the intake valves. GDI engines may also be able to run a higher compression ratio, which would further boost power. More power could mean better fuel economy because the driver wouldn't need to use full throttle as often, and when not on full throttle, the ECU could optimize the AFR for economy as noted earlier.
I'm not an expert at this stuff, and these are just my thoughts. What do you guys think?
I think that when they allow AWD KERS and ban refuelling, that this technology will become necessary. Until then however, fuel economy is not that important when you get to refuel every 20 laps or so.
Don't get me wrong, I understand the economy/fuel weight significance, but until they go all out with the regulations aiming for maximum recovery, minimum fuel usage, GDI seems to be another cool technology that just has to wait.
I am not impressed by how it is today to be sure, but we may see something that is absolutely revolutionary with the 2012 regulations. I sincerely hope that we do!
