Gas direct injection?

[ezcurra]

Hello,

I 've read a couple of threads about the new gasoline direct injection engines some companies are developing, and I don't quite understand what the difference is between these and a regular diesel engine, as gasoline is injected separately in the combustion chamber during the compression cycle, just like a diesel engine. Can someone explain it to me?

Thanks,

Mikel

 

[rbattelle]

Indeed the fuel is injected just like a diesel engine (albeit at much lower pressures). But unlike a diesel, compression ratio is much lower (although pretty high for a spark ignition engine... around 12 or so I think) and the spark still ignites the mix. The fact that it's a spark ignition cycle (Otto Cycle) means it is completely distinct from the diesel cycle.



Direct injection on a spark ignition engine is intended to allow an increase in compression ratio while holding detonation at bay. Since efficiency is a direct function of compression ratio, you can automatically achieve improved fuel economy if you can get the ratio higher. [In fact, if you could operate a spark ignition engine at the same compression ratio as a diesel, the spark ignition engine would achieve better fuel economy... the Otto cycle is more efficient than the Diesel cycle!]



I'm not sure if that helps or makes it even more confusing!



-Ryan

 

[CLiberty]

I`m no expert by any means but I believe the operation is similar to diesel engines, it also allows for a much leaner fuel mixture (`ala diesel). The big problems facing gasoline D. I. are excessive sulphur in the fuel(errr i mean "gas"), esp compared to euro/jap gas. The second big hurdle is NOX production, wich goes hand in hand with the extremely lean fuel ratios DI engines are capable of. I used to work for Mitsubishi and there was rumor that they had wanted to bring a DI engine to the states (I believe they are in use in other Parts of the globe).

 

[Vaughn MacKenzie]

The gasoline direct-injection engines I've read about begin injection about the time the intake valve is closing and ends early in the compression stroke. It operates at only slightly higher pressures than standard gas injection.



You can't make a gasser run like a diesel by injecting near TDC like a diesel. . . gas doesn't light off too well without a spark (which is why a diesel conks out when fed gasoline). I wonder about this though. . gasoline injection near TDC with a spark plug? Heck since I feed the Briggs on my push mower a 100% diesel diet and operate it as a spark-ignited diesel, why not reverse the roles?

 

[swankmetal]

so it's not feasible to DI gas into a high compression ratio engine if the timing/duration/cam were set up right (to get rid of the spark)? my buddy and i were pipedreaming about finding marco, filling up a 3rd gen with gas and having some fun. oh well.



dave

 

[fox]

Vaughn, your mail box is full. PM me about the diesel fed briggs. What mods have been done to it?

 

[Hoefler]

OMC has a 2 stroke outboard engines that are direct injected. The Evinrude line. The gas is injected into a dish in the top of the piston as it comes up on compression as it covers the exhaust ports. It is lit off by a spark at the appropriate timing. It runs exceptionally smoother, and the fuel economy is considerably better. Plus it has meet 2008 emissions since 1996.

 

[RustyJC]

The gullwing Mercedes 300 of the mid-1950's was a direct gasoline injection engine. Ahead of its time, huh?



Rusty

 

[Hohn]

For sure. Of recent note is the GDI engines marketed in Isuzu vehicles. Very impressive.



jh

 

[Jeepmullet]

Rotax made some DI gasoline engines for use in Seadoo applications. it was the 951DI





terrible engine BTW

 

[AGrubbs]

VW has been working on this technology for a while and has several cars out on the market already. . using FSI technology.



Here's a link for some info on some of the latest stuff they have been up to. It has a fuel rail max pressure of 2175 PSI. . on GAS!



I wish we could get some of this tech over here. . they clame 170 HP from a 1. 4L TSI engine. and 38 MPG on the hiway. . Not as good MPG as my TDI but it has about 50 more HP on tap.







AG

 

[CLiberty]

This is a pretty good explanation of how it works and why. Granted the info is a bit dated (96?) but the principles still apply.
http://www.mitsubishi-motors.co. jp/inter/technology/GDI/page1.html

 

[RRoton]

Kawasaki builds a three cylinder direct injection jet ski (ultra 130), which is MUCH better than their carb. equipped model (ultra 150).