PORT vs DIRECT vs DUAL INJECTION - a DETAILED comparison -EVERYTHING you need to know in 1 video
749,481
Published 2022-01-16
So both port and direct injection essentially do the same thing – they inject fuel into the engine to create a combustible air/fuel mixture which when combusted creates combustion pressures which drives the piston downward causing the crankshaft to spin which then ultimately turns the wheels of the car.
As the name implies, port injection, injects fuel into the intake port of the engine, before the intake valve, whereas direct injection injects fuel directly into the combustion chamber, after the intake valves. This means that in the case of port injection you will usually find the fuel injectors somewhere on the intake manifold while in the case of direct injection the injectors will often be either on the valve cover or right underneath the intake manifold bolted to the cylinder head.
Both systems consist of essentially the same parts: a fuel tank, a fuel pump, fuel lines and injectors. However because direct injection injects into the combustion chamber it has to inject against the compression pressures of the engine which means that it must operate at much higher fuel pressures. Direct fuel injection often operates at pressures above 2000 psi or 140 bar. Of course to achieve such high pressures the direct fuel injection system must be more complex. It contains both a low pressure in-tank fuel pump and a high pressure cam-shaft driven fuel pump. The injectors themselves are also much more advanced and expensive because they must be capable of opening and closing extremely quickly against very high fuel pressure. They also need to be capable of surviving the harsh conditions created by combustion since their tips are exposed to it.
Direct injection has the advantage of enabling higher compression ratios because it supplies fresh cool fuel directly into the chamber and it injects it later which means that it spends less time inside the engine which means that it picks up less heat than it would in the case of 'port injection. Less heat means less chances of knock which gives direct injection engines more room to increase the compression ratio which can improve both performance and efficiency.
Another reason direct injection can improve performance and reduce emissions and fuel consumption is its location. Because the injector is inside the chamber it means that the amount of fuel injected is the same as the amount of fuel that gets into its chamber. Port fuel injection injects outside the chamber which means that the amount of fuel released isn't necessarily the amount of fuel that ends up in the chamber. Some of it may stick onto the walls of the intake, some may not make it into the chamber before the valve closes. This reduces injection accuracy and control which can negatively impact emissions and efficiency.
But port injection has the benefit of having the intake valves constantly exposed to fuel, a great solvent. Direct fuel injection never injects onto the back of the valves which over time leads to accumulation of carbon deposits and other gunk from the pcv system. This reduces performance and leads to rough running. Results of prevention methods such as oil catch cans and fuel system additives or valve cleaners are mixed and the need to eventually mechanically clean the valves is inevitable. This of course leads to increased maintenance costs for direct injection engines.
Another potential issue that can occur in direct injection engines is LSPI or low speed pre-ignition. This occurs at low rpm and high load (wide open throttle situations). At low rpm piston speeds are low which leads to poor fuel vaporization in direct injection engines. At the same time the high load means that the ECU instructs the injectors to inject more fuel into the cylinder. The other factor that needs to happen is a particle from the back of the valves or an oil droplet that makes it into the chamber and mixes with the poorly vaporized fuel. The mixture then gets exposed to the very high compression inside gdi engines and boom pre-ignition happens, often leading to catastrophic damage if allowed to persist.
A special thank you to my patrons:
Daniel
Daniel Morgan
Pepe
Brian Alvarez
Jack H
Dave Westwood
Joe C
Zwoa Meda Beda
#d4a #gdi #fuelinjection
00:00 Injection location
02:06 Injecting against compression
04:35 Timing
06:02 Compression ratio
07:48 Knock
10:13 Fuel injected vs Fuel combusted
11:09 Vaporization
13:09 Enough fuel for high rpms?
15:18 Intake valve deposits
17:22 LSPI
19:19 Stack the benefits loose the drawbacks
All Comments (21)
-
Support the channel: driving-4-answers-shop.fourthwall.com/
-
Man every one of your videos gets cleaner and more polished, I've really enjoyed watching the channel grow over time. You present very technical subjects in an interesting way. Thank you for sharing!
-
Honestly, best car and ICE channel out there! Highly detailed and accurate yet understandable Small detail: when a gas is compressed, it doesn't pick up heat because of friction between air molecules when they bump in each other, the bumping itself IS the heat !
-
As a graduate student in a piston engine class, I thank you greatly for this video. It made so many things my professor has been talking about clear. ❤
-
This is the best presentation on ANY subject I’ve heard in all my 70 years. Stunning.
-
You left it implicit that the fuel passing by the inlet port will vaporize and take away substantial amounts of heat from the valve, its seat, the piston top and marginally from the whole combustion chamber. That's also the reason why sometimes the ECU will spray (and waste) MORE fuel than can actually be burnt, especially at high RPM and loads: a rich mixture will directly cool down those parts exposed to the combustion heat, out of the reach of closed circuit cooling system. Conversely, direct injection allows for a leaner charge (lower fuel consumption) and hotter combustion, without incurring in pre-ignition or knock, but this has to be carefully weighted against the thermal limits of the engine components. I find the content on your channel is very well made, complete and pleasing to watch. Cheers from Italy and God bless.
-
Another great and well explained video! I remember the old style Bosch CIS fuel injection from my 1981 VW Scirocco S. It continuously injected fuel into the intake. It didn’t need a mass air flow sensor, just a metal plate that raised when the airflow increased which then allowed the metering valve to open and allow more fuel. It was basically a teetotaler and very ingenious!
-
These are the best videos on YouTube explaining automotive theory
-
After an argument with a friend, i decided to learn more about engines. This video was a great break down that i was able to follow!
-
Such an underrated channel. Amazing work, every video is absolutely didactic.
-
So far you sir are the Best gear head speaker person I’ve ever heard explaining how things work in such a nit and clear way. Thumbs way up!!
-
Excellent explanation, which has helped me tremendously in my business as a fuel Injector technician that cleans and flow tests both port and DI Injectors on a daily basis including piezo technology certification.
-
This is perhaps one of best channels for those who wants to understand concepts of IC engine in simple language
-
I cannot describe in words, how grateful I am for your channel.
-
Good video! Duel injection FTW! The ability to run a high CR and high RPM's without the need for race fuel is nice as is running a high CR and big boost without needing race fuel as well. Help with tuning giving bigger games as you can get more liberal with the tune seeing as you get the advantages of DI and PI, but each one offsets the others disadvantages. Not worrying about carbon buildup on the intake valves is a huge plus for people wanting an efficient and reliable daily drive as well.
-
Trabalho a 32 anos com mecânica e nunca aprendi tanto antes de assistir seus vídeos. Muito obrigado.
-
So much in-depth knowledge on your channel! Best car related channel on YouTube imho! Keep up the good work!
-
For someone whose first language obviously isn't English your videos are absolutely brilliant. Each and every one is an invaluable learning experience, thank you!
-
After watching this video carefully, only one word comes to mind... AWESOME
-
not an engineer or mechanic but this video was so easy to follow and understand. thank you!
