Perkins 4-108 fuel in exhaust

[AlbaDiesels]

Originally Posted by CDK

At idle, injection starts too late, so unburnt fuel leaves the engine. At higher rpm the advance mechanism prevents this.
So the pump needs to be advanced a few degrees against the rotation direction.

Well it's the other way around. Injection timing could be spot on at idle, but as the engine speeds up the IGNITION starts to retard. This is because of the pretty much constant injection lag and ignition delay, and the fact that as engine speed increases, the time available for combustion decreases, so it appears that the point of injection is occurring later (retarding), when in fact, it's always at a constant crank angle. In effect, because of the constant delays due to injection lag and ignition lag, as speed increases the fuel ignition and combustion occurs later and later in the cycle than it should.

The advance mechanism compensates for this by advancing the timing.

Engines with pumps not fitted with an advance mechanism will generally have the timing advanced at idle, and the timing optimised for a particular speed/load. This way the timing 'naturally' retards until it's at the optimum point for the speed, whether thats 1500/1800/3600 rpm for a generator, or for cruising speed or a set speed for a CP prop, or whatever.

If the pump is fitted with an advance mechanism, then failure would cause smoking, excessive fuel consumption and loss of power.

Running the engine at idle (low loads) for periods of time can cause the problem of fuel in the exhaust (wet stacking), partly because the engine cools down. I see this all the time in engines such as Kelvins.

[CDK]

Originally Posted by AlbaDiesels

Well it's the other way around. Injection timing could be spot on at idle, but as the engine speeds up the IGNITION starts to retard. This is because of the pretty much constant injection lag and ignition delay, and the fact that as engine speed increases, the time available for combustion decreases, so it appears that the point of injection is occurring later (retarding), when in fact, it's always at a constant crank angle. In effect, because of the constant delays due to injection lag and ignition lag, as speed increases the fuel ignition and combustion occurs later and later in the cycle than it should.

I was not lecturing about diesel engines in general, just finding an explanation for the behavior of this particular one.
Believe it or not, I know quite well how engines work and so do you.

When responding to a question we have to rely on the data supplied, unless that is obviously wrong. If a rebuilt engine with only 400 hours keeps expelling unburnt fuel at idle only, the injection and hence the combustion starts too late. At higher rpm an advance mechanism will improve that. With an engine idling at only 450 rpm, the timing -when set correctly- will always be fairly late.

There are many other possible causes like a burnt or damaged exhaust valve, broken rings or an injector that doesn't close, but then the question should have started with a different engine story, like just rebuilt or a very worn, neglected one.

[kanev]

Hi CDK
Will it be enough power if I install diesel engine (VW golf 1986 NON turbo 1.6)
On bayliner with cuddy 17ft long(1989) ????????
THANK YOU
ALEX

[pistnbroke]

CDK is right it needs the pump moving a few degrees in the opposite direction to the pump drive rotation. this will allow the fuel to be burnt fully before the exhaust valve opens ...I think what Alba diesels is saying is probably right ...if its not advancing then it is retarded relative the the correct igniton positon....Ist all a queston of where you start and what logic framework you are using ...

[pistnbroke]

kevan a 17 ft needs about 100 hp if you are going to get up on the plane and do about 40 kts .....so your 1.6 produces what 60 hp ??? so know you know where you are .....for a canal ok for the open water underpowered ..

[CDK]

Originally Posted by kanev

Hi CDK
Will it be enough power if I install diesel engine (VW golf 1986 NON turbo 1.6)
On bayliner with cuddy 17ft long(1989) ????????
THANK YOU
ALEX

You will have insufficient power to plane unless you have the passengers move forward when the boat tries to climb out.
A VW1.9 from a Passat (AAZ) or from a van (ABL) does it much better. Size and weight are about the same.

[kanev]

Originally Posted by CDK

You will have insufficient power to plane unless you have the passengers move forward when the boat tries to climb out.
A VW1.9 from a Passat (AAZ) or from a van (ABL) does it much better. Size and weight are about the same.

thank you