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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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05-19-2012, 06:37 PM | #1 |
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Gasoline Direct Injection...
I was wondering if anyone has any experience with Toyota's GDI systems that coluld give me some knowledge on the philosophy of the technology. My guess is it's all about getting close to stoichiometric burn without sacrificing torque?
Another thing that's kind of eluding me is the direct injections themselves. I know the already high Compression Ratio of the D4S system is to compensate for the lean port injection, and to actually get flame propagation after spark; but is there room to increase injection pressure, duration and volume to get more torque and power out of the bottom end? I also assume due to the nature of direct injection, you could probably increase CR at the same time to get a more energetic burn? (just so long as your port charge isn't detonating) Not exactly experienced with GDI systems so all insight would be extremely helpful. Much Appreciated, -Doog |
05-19-2012, 06:43 PM | #2 |
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Because titanium. Last edited by Dimman; 05-19-2012 at 06:46 PM. Reason: link |
05-19-2012, 07:16 PM | #3 |
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You sound like you think there's a lack of fuel delivery or something...that's not true at all. The direct injectors are capable of supplying all the fuel.
I'm not 100% sure but I believe the few important advantages of direct injection are as follows: 1. Increased charge cooling and thus improved efficiency, by allowing the intake air to absorb more of the latent heat of vaporization (not sure to what degree this happens, as port injection can spray onto the valve and it seems unlikely that the heat on the valve could cause the fuel to vaporize...perhaps someone else could give some input on this). I imagine that at part load operation, injecting the fuel later in a DI system allows a greater efficiency improvement...again not totally clear on how much of a difference this makes. 2. Allowing "stratified charge", since the fuel is placed directly inside the cylinder at flexible timing you can get more fuel around the spark plug. I imagine there's also the ability to cool hot spots on the piston down. The reason for D4-S is explained in the papers that arghx7 provided. In short, direct injection has a harder time forming a homogeneous mixture because there's less time for it, so DI engines usually have high tumble ports, which restricts airflow at high engine speeds. To get more power, you need more airflow at high revs, so they fitted higher flowing ports onto the 2GR-FSE, and used port injectors to help low end combustion. |
05-20-2012, 03:37 PM | #4 | ||||
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Quote:
Below is a chart from a very recently published study from the Sloan Automotive Laboratory at MIT. It examines the cooling effects of direct injection under WOT operation. The study took a Pontiac Solstice engine (direct injected 2.0 liter turbo) and equipped it with port injectors. They figured out an average combustion chamber pressure trace at a borderline knocking condition using direct injection only and then port injection only. Then they heated up the intake air and tried to figure out how much hotter the intake air has to be for direct injection to have the same knock characteristics as port injection. The method was used to calculate "effective charge cooling" of direct injection, especially with ethanol fuels. Quote:
Quote:
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Last edited by arghx7; 05-20-2012 at 03:47 PM. |
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The Following User Says Thank You to arghx7 For This Useful Post: | Dimman (05-20-2012) |
05-21-2012, 01:34 AM | #5 | |
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Quote:
Arghx7 and Killer, thanks for the explanations, it's very clear this tech works a LOT differently than what was explained to me. |
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05-21-2012, 02:05 PM | #6 |
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There's a lot of confusion and misinformation circulating about direct injection in its various forms.
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