Why Direct Injection Develop Carbon Deposits

[CELICA_XX]

I thought this was a decent article, with all the talk about DI engines and how that relates to different OCI's

Why Direct Injection Engines Develop Carbon Deposits:

http://www.import-car.com/why-direct-injection-engines-develop-carbon-deposits/

 

[millerbl00]

DI has been around since 1997 and it still has bugs. That's way I say don't jump on this new tech too soon and be a beta tester!

 

[weasley]

So one wonders why diesel engines don't suffer intake valve deposit problems in the same way? DI has been around for WAY longer than 18 years!

 

[xxch4osxx]

Originally Posted By: weasley
So one wonders why diesel engines don't suffer intake valve deposit problems in the same way? DI has been around for WAY longer than 18 years!
That is something I have also wondered. Why is it just the gas engines having these problems? If direct injection is so much more precise in fuel delivery, how are these DI engines having fuel dilution problems?

 

[Rand]

I think in general its all the beta testing going on by consumers in the search for higher CAFE.

For example Subaru's very low tension rings in a horizontally opposed 4 cylinder. I'm sure other manufacturers are going to similar rings or already have. This might make it easier to get unburnt fuel past the rings eh?

 

[Pontual]

I Don't agree with what the article says:

"Carbon deposits cause the air to tumble into the combustion chamber, and this turbulence causes the fuel and air mixture to be unevenly distributed. When ignited, the flame front can be erratic, leave unburned fuel and create hot spots in the combustion chamber."

That's contrary to the engineering knowledge, since cc turbulence always was a factor for a better fuel/air steer and also more complete mixture burn. Maybe the aerodynamic term turbulence was misplaced for "boundary layer" or even "laminar flow" interactions. Bad technics.

 

[ARCOgraphite]

I would think the cam timing on the diesel is MUCH more conservative than the gas. Also, diesel are not throttled. I can only conject that with the late fuel injection and instant phase change due to HTHP on a gasoline engine you are loosing the fuel hydrodyn seal at the top two rings at COMP phase and relying only on oil control to prevent leakdown.

 

[440Magnum]

Originally Posted By: weasley
So one wonders why diesel engines don't suffer intake valve deposit problems in the same way?


No mystery there at all. Diesel engines have no throttle blade in the intake path, the air velocity and volume flow over the stem of the intake valves is high all the time- even at idle. there's virtually no reversion flow out of the cylinder into the intake, no vacuum in the intake, and the intake is comparatively cool with fresh air constantly sweeping through. Even in a turbo application where the intake air can be very hot, there's no vacuum and little reversion.

A GDI engine has a throttle, so at idle there is very little airflow, a lot of reversion (back-flow) out of the cylinder and into the intake that can even include exhaust gasses from the previous combustion cycle, and there's a high vacuum condition in the intake that draws oil past the intake valve stems and into a hot, stagnant, condition that's ripe for cooking it to hard carbon deposits.

 

[BMWTurboDzl]

Originally Posted By: weasley
So one wonders why diesel engines don't suffer intake valve deposit problems in the same way? DI has been around for WAY longer than 18 years!


Light truck and passenger car diesels DO get intake build up. It's a mixture of soot(EGR) and condensed blow-by gases.

OTR rigs not so much because they run at full power most of the time.

Google "335d carbon build up"

 

[KrisZ]

Light duty diesels do have carbon deposit problems. Why do we not hear about them? Light duty diesel engines have something like 3% market penetration.

 

[Silk]

Intake deposits are very common on modern common rail small diesels. They have EGR and throttle bodies, a thick jelly like goop forms, I've seen intakes reduced by 50%.

 

[Bluestream]

Originally Posted By: millerbl00
DI has been around since 1997 and it still has bugs. That's way I say don't jump on this new tech too soon and be a beta tester!


Been around since 97 so I wouldn't call it new. Reminds of when FI became popular, the old timers still wanted the carb engines...

 

[OVERKILL]

It has been around a LOT longer than 1997:

Quote:

Direct gasoline injection was applied during the Second World War to almost all higher-output production aircraft powerplants made in Germany (the widely used BMW 801 radial, and the popular inverted inline V12 Daimler-Benz DB 601, DB 603 and DB 605, along with the similar Junkers Jumo 210G, Jumo 211 and Jumo 213, starting as early as 1937 for both the Jumo 210G and DB 601), the Soviet Union's (Shvetsov ASh-82FN radial, 1943, Chemical Automatics Design Bureau - KB Khimavtomatika) and the US (Wright R-3350 Duplex Cyclone radial, 1944).

The first automotive direct injection system used to run on gasoline was developed by Bosch, and was introduced by Goliath and Gutbrod in 1952. This was basically a high-pressure diesel direct-injection pump with an intake throttle valve set up. (Diesels only change the amount of fuel injected to vary output; there is no throttle.) This system used a normal gasoline fuel pump, to provide fuel to a mechanically driven injection pump, which had separate plungers per injector to deliver a very high injection pressure directly into the combustion chamber. The 1955 Mercedes-Benz 300SL, the first production sports car to use fuel injection, used direct injection. The Bosch fuel injectors were placed into the bores on the cylinder wall used by the spark plugs in other Mercedes-Benz six-cylinder engines (the spark plugs were relocated to the cylinder head). Later, more mainstream applications of fuel injection favored the less-expensive indirect injection methods.


http://en.wikipedia.org/wiki/Gasoline_direct_injection

 

[demarpaint]

Originally Posted By: BMWTurboDzl


Google "335d carbon build up"


Wow What an expensive mess............

 

[Michael_P]

Quote:
No mystery there at all. Diesel engines have no throttle blade in the intake path, the air velocity and volume flow over the stem of the intake valves is high all the time- even at idle.


I have seen butterfly vales in throttle bodies of newer diesels, particularly common rail. I'm fairly certain my (wifes) X5 diesel has a butterfly valve. Seems silly it being a diesel, but now I am wondering if I will have carbon build up over time. Just googled 335d carbon build up.

 

[BMWTurboDzl]

Originally Posted By: Michael_P
Quote:
No mystery there at all. Diesel engines have no throttle blade in the intake path, the air velocity and volume flow over the stem of the intake valves is high all the time- even at idle.


I have seen butterfly vales in throttle bodies of newer diesels, particularly common rail. I'm fairly certain my (wifes) X5 diesel has a butterfly valve. Seems silly it being a diesel, but now I am wondering if I will have carbon build up over time. Just googled 335d carbon build up.


That valve is there for emissions and will also prevent a runaway condition. Also your diesel has 2 EGR's (Low & High Pressure). The 335d had only the HP EGR.

 

[Nick1994]

Originally Posted By: weasley
So one wonders why diesel engines don't suffer intake valve deposit problems in the same way? DI has been around for WAY longer than 18 years!
Diesels do get deposit problems

 

[millerbl00]

If you can't get it right after 18 years time to move on...

 

[whip]

Originally Posted By: millerbl00
If you can't get it right after 18 years time to move on...

To newer tech that you can spend your time worrying about? What do you want them to move on to?

 

[Mykl]

Originally Posted By: millerbl00
If you can't get it right after 18 years time to move on...


Man, by that logic we should completely give up on internal combustion engines entirely. Those things are nothing but trouble.