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Old 30th August 2009, 19:42   #1
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Default Direct Injection engines for Petrol !!!

Just saw the below snippet on Mercedes-Benz website the new C250 used direct-injection petrol engine. I was under the impression that DI engines were primarily diesel technology.
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Never content to rest on our laurels, we’ve added a second highly economical BlueEFFICIENCY engine to the C-Class Estate’s petrol line-up. Like the existing
C 180 K BlueEFFICIENCY, the new C 250 CGI BlueEFFICIENCY is designed to optimise environmental protection.

Replacing the 6-cylinder C 230 unit, the C 250 CGI BlueEFFICIENCY uses the latest direct injection technology to maximise performance. A 4-cylinder unit, it still produces 204 hp and the associated weight savings help cut fuel consumption.
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Here is the link to the merc website
Mercedes-Benz UK - Overview - Engines

This is supposed to improve efficiency and reduce carbon footprint of the vehicle.
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Old 30th August 2009, 19:51   #2
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They've been around for some time. I remember some 10 plus years back Mitsubishi were one of the first ones to come up with one of those, calling it GDI, Gasoline Direct Injection. Subsequently not much was heard of from this tech, but now I believe its fairly common, with the likes of Audi using it in their line up.
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Old 30th August 2009, 20:02   #3
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Can someone throw some light on the difference between MPFI and Direct Injection.

Cheers
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Old 30th August 2009, 20:06   #4
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GDI

In a nutshell, this is pretty much CRDi tech in petrol engines. Common rail, high pressure fuel, injected straight into the cylinders instead of MPFI where the fuel is injected after the intake manifold.

The main advantage is that it allows much leaner combustion ratios ('lean burn') during low engine loads and precise injection control allows for tighter emissions. The pros and cons therefore are similar to CRDi too.

Last edited by ImmortalZ : 30th August 2009 at 20:09.
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Old 30th August 2009, 20:28   #5
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Here is what is different in a gasoline direct injection engine:
In a 'normal' MPFI injection, fuel mixture formation usually (only possible exception being simultaneous port injection wherin for at least one of the cylinders, spray targeting may be directly into the open intake valve and the fuel and air mix at the boundary of intake port and cylinder) takes place outside the cylinder, in the intake port since the injector is located in the inlet port. Therfore the mixture that enters the cylinders is already 'pre-mixed' or uniform.
When you are demanding very little power from the engine, fuel supply has to be reduced. However since there is minimum limit to the concentration of fuel in air below which the fuel would not burn (or would burn producing lots of NOx pollutants), the air supply has to reduce in sync with it. So the throttle butterfly has to be closed, thereby reducing the air supply.
So far, so good??? NO! Because the air supply and fuel supply have to be reduced in sync, there is a lot of throttling loss, wherein the engine is wasting mechanical energy in sucking against a closed throttle butterfly.
Enter FSI/GDI: Here the mixture formation occurs inside the *cylinder* instead of the intake port. So inside the cylinder, the charge need not be uniform. So when you demand very limited power from the engine, there can be small area near the spark plug where the fuel/air mix is stoichiometric (Lambda = 1), while the rest of the cylinder can be full of air (or better still, exhaust gases). So you don't have close the throttle butterfly as much.
So, in GDI/FSI, you can have extremely lean-burn (Lambda> 10) and dethrottle the engine at the same time.
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Old 30th August 2009, 21:41   #6
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Wouldn't you have a problem at higher RPMs with the fuel not atomising?
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Old 30th August 2009, 21:53   #7
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Which is why rail pressure in GDI systems is much higher, so that the droplet size can be much smaller for the same injection quantity.

In an indirect injection (MPFI) system, the fuel pump output is around 600kPa. In the latest 2nd generation Demand Controlled GDI systems (employing HDP5 - HochDrukePumpe5) the output pressure is as much as 20mPa.

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Old 30th August 2009, 22:04   #8
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A DI engine injects the fuel directly into the cylinder (similar to diesel DI as pointed out by GTO). An MPFI engine injects fuel into the manifold just before the inlet valve. This allows more precise metering. Also, as teh cylinder space is taken up only by air you get more power. This is esp. true with gas powered cars as the fuel to air ratio has much more volume of the fuel. A Hydrogen car will require half molecule of oxygen for every one of hydrogen. This H:O ratio will be 2:1. With 20% Oxygen in air you will still require 2:5!
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Old 31st August 2009, 10:14   #9
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Last that I read C250 claimed a fuel efficiency of 15KMPL which is pretty impressive for a output of that range.
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Old 31st August 2009, 10:34   #10
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So what I understand from this is GDI engines are efficient compared to MPFI.
Is GDI and FSI/TSI also same?
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Old 31st August 2009, 11:16   #11
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Direct injection has been here from quite some time now.
Now even Porsch has introduced all of its 2009 models with direct fuel injection (DFI).
This direct injection technology is at its best. More power, more fuel economy.

Instead of me explaining, go through this.


The fuel injection types used in newer cars include:
* Single-point or throttle body injection (TBI)
* Port or multi-point fuel injection (MPFI)
* Sequential fuel injection (SFI)
* Direct injection

Single-point or throttle body injection (TBI)
The earliest and simplest type of fuel injection, single-point simply replaces the carburetor with one or two fuel-injector nozzles in the throttle body, which is the throat of the engine’s air intake manifold. For some automakers, single-point injection was a stepping stone to the more complex multi-point system. Though not as precise as the systems that have followed, TBI meters fuel better than a carburetor and is less expensive and easier to service.

Port or multi-point fuel injection (MPFI)
Multi-point fuel injection devotes a separate injector nozzle to each cylinder, right outside its intake port, which is why the system is sometimes called port injection. Shooting the fuel vapor this close to the intake port almost ensures that it will be drawn completely into the cylinder. The main advantage is that MPFI meters fuel more precisely than do TBI designs, better achieving the desired air/fuel ratio and improving all related aspects. Also, it virtually eliminates the possibility that fuel will condense or collect in the intake manifold. With TBI and carburetors, the intake manifold must be designed to conduct the engine’s heat, a measure to vaporize liquid fuel. This is unnecessary on engines equipped with MPFI, so the intake manifold can be formed from lighter-weight material, even plastic. Incremental fuel economy improvements result. Also, where conventional metal intake manifolds must be located atop the engine to conduct heat, those used in MPFI can be placed more creatively, granting engineers design flexibility.

Sequential fuel injection (SFI)
Sequential fuel injection, also called sequential port fuel injection (SPFI) or timed injection, is a type of multi-port injection. Though basic MPFI employs multiple injectors, they all spray their fuel at the same time or in groups. As a result, the fuel may “hang around” a port for as long as 150 milliseconds when the engine is idling. This may not seem like much, but it’s enough of a shortcoming that engineers addressed it: Sequential fuel injection triggers each injector nozzle independently. Timed like spark plugs, they spray the fuel immediately before or as their intake valve opens. It seems a minor step, but efficiency and emissions improvements come in very small doses.

Direct injection
Direct injection takes the fuel injection concept about as far as it can go, injecting fuel directly into the combustion chambers, past the valves. More common in diesel engines, direct injection is starting to pop up in gasoline engine designs, sometimes called DIG for direct injection gasoline. Again, fuel metering is even more precise than in the other injection schemes, and the direct injection gives engineers yet another variable to influence precisely how combustion occurs in the cylinders. The science of engine design scrutinizes how the fuel/air mixture swirls around in the cylinders and how the explosion travels from the ignition point. Things such as the shape of cylinders and pistons; port and spark plug locations; timing, duration and intensity of the spark; and number of spark plugs per cylinder (more than one is possible) all affect how evenly and completely fuel combusts in a gasoline engine. Direct injection is another tool in that discipline, one that can be used in low-emissions lean-burn engines.
Source: ask.cars.com
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Old 31st August 2009, 11:27   #12
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Quote:
Originally Posted by MileCruncher View Post
Is GDI and FSI/TSI also same?
As far as I understand, FSI is VW's trade/brand name for GDI. VW also called it 'Iniezione Diretta Stratificata' on the Lamborghini Gallardo.

On Dante's reply: I think one of the early Astras had Single point fuel injection, did it not? Any examples of Group Fuel Injection?

Last edited by vipul_singh : 31st August 2009 at 11:36.
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Old 31st August 2009, 15:33   #13
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My Uno 1.2 has Single Point Fuel Injection
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Old 31st August 2009, 16:31   #14
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Indeed the original Astra and the Uno have SPFI. Opel got so bugged by the MPFI failures in early Cielos that the opted out of this technology in the beginning. Later Opel did introduce the Astra with MPFI.

With FI and ECU it is easy for the vendor to offer the same engine in different states of tune. The future will almost certainly be DI unless something better shows up.
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Old 31st August 2009, 17:41   #15
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If GDI is about fuel injection, I think the next step is controlled air mass.

I expect FIAT's MultiAir to be the next big thing after CRDI and GDI. And this time, FIAT has clarified that they would not sell the rights to MultiAir like they sold CRDI to Bosch for cash.
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