PFI vs GDI

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I was just observing the pictures below, how come it took several decades until someone finally got a better idea on the fuel delivery from PFI to GDI by simply re-arranging the fuel injector directly into the internal combustion chamber? It looked so simple and yet the answer is just around the corner just by glancing at the pictures.

pfi-line.jpg


gdi-ine.jpg
 
Direct injection requires much higher pressure and is more expensive to implement, GDI engines have greater problems with soot and fuel dillution, manufacturers have mostly started using GDI engines because the increase fuel economy and reduce CO2 emissions, although they have much worse particle emissions.
 
Direct injection requires much higher pressure and is more expensive to implement, GDI engines have greater problems with soot and fuel dillution, manufacturers have mostly started using GDI engines because the increase fuel economy and reduce CO2 emissions, although they have much worse particle emissions.
By glancing at pictures, it looks to me the GDI has the advantage in fuel economy by directly injecting the fuel into the chamber whereas PFI injects the fuel in to intake valve with the chance of fuel evaporating before it goes in to the chamber.
 
It took several decades for computing power to develop to the point where GDI benefits could be fully realized. In today’s GDI engines, each power stroke may involve multiple injections of fuel in each cylinder at varying times, all depending on conditions and demands.
 
I was just observing the pictures below, how come it took several decades until someone finally got a better idea on the fuel delivery from PFI to GDI by simply re-arranging the fuel injector directly into the internal combustion chamber? It looked so simple and yet the answer is just around the corner just by glancing at the pictures.

pfi-line.jpg


gdi-ine.jpg

Because they couldn't get it working reliably. It's actually very old tech, much like the first cars were EV.....
 
You guys know that gasoline particulate filters are already on a few vehicles to reduce emissions and could be on all future gasoline vehicles eventually.
 
Not a new concept. Diesel engines inject fuel right into the combustion chamber also. EVs sort of inject electricity directly into a motor. Of course it has no valves or combustion. Each configuration has positive and negative aspects.
 
DI is NOT new or better mercedes used it in the 50's + it shoul have stayed there BUT today its hard to find a newer one without + using both can be better but NOT perfect + only a few manufactureres do due to $$$$. DON't own or want DI or a CVT + being 74 YO i can prolly do WITHOUT!!
 
By glancing at pictures, it looks to me the GDI has the advantage in fuel economy by directly injecting the fuel into the chamber whereas PFI injects the fuel in to intake valve with the chance of fuel evaporating before it goes in to the chamber.

Because in DI engines the fuel evaporates in the combustion chamber, the combustion chamber is cooler, allowing a higher compression ratio which produces better fuel economy. For example, my 2015 DI Honda has a compression ratio of 11.1:1 and runs on 87 octane. Not possible with port injection.
 
The physical implementation of modern GDI has only been possible since the late-90s, which is really tied to the widespread adoption of common-rail direct-injection diesel.

Prior to common rail, diesels used a distribution-pump or camshaft-actuated unit injectors. For everyone talking about how direct injection "isn't new" and Mercedes was using it ages ago, that's mechanical fuel injection and actually not too far off from pre-common-rail distribution-pump diesel. Saying the system that Mercedes used long ago is like today's systems is showing a fundamental misunderstanding of how both current and past systems work.

Anyway, the move from distribution pump to common rail in diesels was predicated by the introduction of a electronic fuel injector that could live in a very high pressure fuel environment and be controlled precisely enough for the application. These first ended up in diesels primarily because of emissions. While early electronic fuel injectors could fuel an engine, it couldn't do it very cleanly. Diesels, naturally having looser emission standards, could get way with being dirty. There was no way a GDI engine with that technology would meet even the minimum Tier 2 Bin 5 federal emission minimum of the era: Too much HC and too much NOX.

Following the diesel story come the introduction of piezo injectors. These are what brought the fine control for fueling strategies with the ability for multiple pulses and actuations in a single combustion event. This was the big enabler for GDI engines. Injectors were now capable of fueling an engine and meeting emissions with elaborate multiple-pulse injection strategies. Someone also mentioned power required to process and command such strategies, which is part of this story too, for both diesels and gas engines.

Injecting fuel directly into the combustion chamber was, as a concept, something that researchers knew for a very long time would provide significant benefits but the technology required to implement matured in stages. Diesels first moved from indirect-injection to direct-injection while still using distribution-pumps, then technology allowed the use of a common-rail and electronic injectors, then piezo injectors. An analog is to look at cylinder deactivation: GM did it in the early-80s and it failed because, while the concept was sound, the technology wasn't robust enough to implement. 40 years later, it's common.
 
I was just observing the pictures below, how come it took several decades until someone finally got a better idea on the fuel delivery from PFI to GDI by simply re-arranging the fuel injector directly into the internal combustion chamber? It looked so simple and yet the answer is just around the corner just by glancing at the pictures.

pfi-line.jpg


gdi-ine.jpg
First, I'm going to take issue with your premise that this is a better idea. It's not, it's a different approach that has some advantages and some disadvantages, some of them significant.

PFI, in an MPFI/SEFI arrangement, injects the fuel into a moving column of air, which results in a nearly perfect homogenous charge of fuel and air, which is then compressed and ignited. This is extremely clean, but, since you can't control when the fuel is mixed with the air, your only levers for adjustment in mitigating knock are through ignition timing and enrichment.

GDI injects fuel directly into the chamber. This clearly results in a less homogenous mixture. However, the fuel charge has a cooling effect, lowering knock propensity, AND, you can choose WHEN to inject the fuel, another key function in mitigating knock, facilitating the use of higher compression ratios. This means you can get away with a wider range of mixtures as well. All of this works together to improve fuel economy under certain driving conditions and, when coupled with forced induction, can increase power output over port injection. Not spraying the fuel into the intake charge means that deposits can build-up on the back of the intake valve and the high pressure spraying of fuel, hitting the wall and condensing, coupled with the liberal use of enrichment and fuel cooling for knock mitigation means significant fuel dilution of the oil in many applications.
 
My limited knowledge on this topic is that they were able to get Diesels to work with direct injection 80 years ago because diesel is a lubricant in itself. Gasoline is not, and it would destroy the injectors in short order.

There were mechanical direct injection gasoline systems decades ago - as mentioned, but the materials required to make them last didn't exist. Not to mention adding all that mechanical tech for direct injection was a lot of work for minimal gain.

You could make a pretty good argument that its a lot of complexity and potential maintenance problems for minimal gain even today, for normal - non performance applications.
 
Additional note; there are several OEMs that employ both technologies for the benefits each can provide. Check out the attached video for more detail.
 
Because in DI engines the fuel evaporates in the combustion chamber, the combustion chamber is cooler, allowing a higher compression ratio which produces better fuel economy. For example, my 2015 DI Honda has a compression ratio of 11.1:1 and runs on 87 octane. Not possible with port injection.
The 3.6 Penastar PUG engine in my '20 Jeep has a compression ratio of 11.3:1 and is MPFI. It runs on 87 octane as well.
 
Additional note; there are several OEMs that employ both technologies for the benefits each can provide. Check out the attached video for more detail.

This is a relatively recent development though. Historically, Toyota was the only one that used these system in parallel and then Ford hopped on the bus.

I should also note that fuel dilution levels vary wildly between OEM's. Ford and VAG have had some decent issues with it (particularly early on) but Honda is by far the worst, based on the UOA's we've seen. BMW on the other hand seems to have the lowest levels.
 
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