Direct Injection Diesel Engine

You have commited a sin by not mentioning if this engine is 2 cycle or four cycle, or what the engine configuration is1, 2, 3, 4, 5, 6, 7, or an 8 cylinder or larger v block or inline, or horizontal, or whether it is air cooled or water cooled or for that matter the brand of engine!

Rule number one-those are burn marks from the compression and explosion of the diesel fuel in the cylinder! The bowl in the piston is there to allow expansion of the gasses and the resulting pressure to force the piston down on the power stroke

You will have unburned diesel fuel from the shut down anyway so do not mess with it!!!!!!!!!!!!!!! If you are that worried replace all the injectors with new injectors and injector parts.

Unlkess you have white smoke which is a direct indication of incomplete combustion dont worry about it!!!

Indirect injection diesel engines are so much simpler.:^)

This is an 12 cylinder, V block, four stroke, direct injection diesel engine (earth moving type) air cooled.

Is the injector suppose be spray inside the bowl or not? It seams as if the injector sprays on top of the piston crown if looking at the burning marks equally spaced on the piston crown, the same as the injector nozzle orifice holes.

The burn pattern is correct.

Mentioning the engine maker and model, as well as 2 or 4 stroke and cooling method would certainly help, while number of cylinders and arrangement (in-line/vee/flat) is quite irrelevant. Is the company or person who did the upgrade still available? If there is no reliable timing data available for the current state of tune, a competent diesel specialist and an indicator to log the pressure vs. crank angle is needed. HTH Ulrich

This question of timing must be sent to the manufacturer. The local dealer will be able to answer this also. Is this a Duetz?

Our answers will only be rough, and improper timing will greatly effect fuel consumption, heat loading on the piston crown, and more importantly ignition delay. Ignition delay is the killer. I'm a diesel engine power consultant and with all my experience I wouldn't try to answer this question.

The marks on the piston top are normal. The injection pressure is 800 to 1200 barg (for small engines) at full load so this is a very violent spray action which marks the piston top. It has a cleaning action so the burn marks will be brown or grey while the balance of the crown will be black. The angle of how the spray enters the swirl chamber (bowl of the piston crown) is critical and a very intentional design. If the angle is too great, the spray hits the cylinder liner (I've seen spray cuts on a cylinder liner). If the angle is too shallow, it will cut the piston crown. The fuel must burn efficiently when injected to prevent 'jet cutting' so the angle trys to contact the hot air swirl and promote what is termed a flame front to continue the burn in a swirl chamber. That is why direct injection pistons have this bowl design where the compressed air swirls waiting for fuel to enter.

Direct injection is much better than pre-combustion designs as we can get more power, much better fuel emissions, much better economy, easier starting, higher RPM (power increases with the square of the speed) and other benefits. The old pre-cup designs were primarily designed for ugly fuel quality 35-50 years ago, low RPM (we didn't know how to balance masses or had materials for a large high speed with all those G forces inside) and also because we didn't know how to burn all the fuel in a large open chamber (direct injection) completely as we do today. Pre-cups prevented ignition delay as the fuel was 75% burned before jetting into the main combustion chamber to finish the burn. Too bad the pre-cup itself up in the head had to be water cooled so we the fuel heat value went into the cooling water instead of out to 'work'.

Thank you for feedback. The injector pressure is 240 bar, supplied by a rotary mechanical injection pump. This is a large diesel engine, max power at 2200-2400 rpm.

Will you still see 8x burning marks on the piston crown outer edge if the injector nozzle sprays in the bowl (swirl chamber). I thought that if the nozzle sprays inside the bowl only an atomised miss will burn on top of the crown, therefor you will not see 8x defined burning marks on top of the crown.

My opinion is the location of the marks is incorrect if they are on the edges of the piston (the flat top near the liner). The marks should begin near the center and streak outwards but be 100% in the bowl. Check your liner for small pits. Send me a pic. I'll email you privately. Is this a Duetz diesel? I have connections at Duetz. Large Air Cooled V-12 tells me Duetz. If the burn marks are wrong, the timing could be off by 20* or more (but there is no way it would run) but likely someone put the wrong injector tips in during a rebuild. I don't have too much small engine experience. My normal engines are http://www.wartsila.com/Wartsila/global/docs/en/ship_power/media_publications/brochures/product/engines/medium_speed/w64_tr.pdf

I agree that it is duetz but all the duetz engines I ever worked on had a three leaf clover depression in the piston head.

Please tell us more about the engine. To me it sounds like a Detroit Diesel (two stroke). You could have any of a number of difficulties especially if the engine has been rebiult with different model parts. You need to find a mechanic that is more than 50 years old with a vast history for your engine type.

Your inquiry describes a problem usually describing an injector problem or a bad turbo/supercharger. Iether of which look like a timing problem.

I don't know much about diesel combustion but I visited the Tatra factory many years ago in Czechoslovakia who produce trucks with air cooled 'V' engines (8,10,12cyl I think), famous for their durability and successes in the Paris-Dakar. I was working on their cabs. Marks on the piston crown sound pretty normal. Has it run many hours(1) and is there any indication of actual damage(2)? If the ansers are (1)=yes and (2)=no I woudn't worry. Beyond that it sounds like you need a (large) dyno!