How do you define "clog" and "often"?
And what are the symptoms in engine operation you have related to "clog"?
When you remove fuel injectors of used DI diesels, regrdless of either ones from traditional pump-line-nozzle system or ones from state-of-arts common rail system, you usually observe carbon deposits at the tip of the nozzles. However, I do not have encountered a situation where the carbon deposits blocked fuel flow to the extent that engines had lost power. Some experience I have is partial blockage of nozzle holes (their diameters are in the range of 100 to 150 microns) caused by zinc deposits. Becasue this deposit reduces flow area, the power output comes down. We had debates on where the zinc had come from with fuel system suppliers, and most often what we hear is the source of zinc is either from fuel lines or fuel tanks which OEMs have the responsibility on design. But I do not think this phenomenon goes well with the description of "often" becasue once it happened it usually stays there.
thank you for your answer Mr.Hirofumi Kizawa ,here i want to mention that the engine is not yet installed in a vehicle it was tested at our test cell,moreover the Nozzle opening pressure of the mentioned injectors is around 240-255 bar and i'm expecting a suggestion to avoid clog of the nozzle orifice due to carbon deposition
Mr. Prashanth Muthu,
I suppose you are facing practical problems rather than something about scientific investigation. So, you would need engineers than university professors or research professionals. It would be very helpful if you could provide us more information. In what operating conditons have you faced nozzle clogging? How many injectors clogged if you ran a multi-cylinder diesel engine? How often did you find nozzle clogging? How did you detect the nozzle clogging, in other words what were the symptoms that made you judge nozzle clogging might have happened during engine operation? What are the nozzle specifications other than needle opening pressure, such as the nozzle hole size, the number of holes and "nozzle sac volume"? How much nozzle tip protrusion is your engine set (, the nozzle tip protrusion is defined as the distance to the tip of the nozzle from the fire face of the cylinder head)? If you removed problematic nozzles out of the cylinder head and investigated them, how many nozzle holes were clogged? Can you share fuel specifications?
When you remove diesel injection nozzle and see them, you most likey observe that their tips are covered by carbon. However, this covering by carbon does not necessarily mean nozzle holes are clogged. You can see very tiny holes in the mounds of carbon at the nozzle tips. These carbon mounds at the tips of nozzles form with many reasons. Poor atomization of fuel especially around the end of fuel injection or trapped fuel in the "nozzle sac" leaks out due to heating can be sources of fuel that can remain on the surface of the nozzle tips and is coked, and this leads to carbon accumulation. However, keep running the engine seems to maintain some level of passage in the carbon mound and neither complete plugging of the passages nor leading to nozzle hole blockage seems to happen, at least in my experience. This sometimes is suspected as a cause of an increase in smoke emission, though. If this type of phenominon is what you are observing, poor atomization of fuel even during "NEW" and the nozzle tip being exposed relatively high temperature due to large protrusion of nozzle tips might be what you may want to check.
Nozzle holes actually clogg in the fields. As I mentioned before, fuel additives or coating materials, usually metals, in the fuel system, inside of high pressure line, low pressure line and fuel tanks, somehow oozed out into fuel and are carried to the injection nozzles, then physically absorbed inside the tiny nozzle holes. Although I have never seen nozzles whose holes are completely plugged by those metals but seen ones bad enough to decrease the amount of fuel injection per stroke, which means less power and operators noticed. I have never experienced this type of problem with carbon and for the metal clogging to become noticeable to operators it takes long hours of operation.
This is as much as I can say at this moment.
I am not sure my comments do any good to you, but if you could share more details of yours, I might be able to be a little bit more helpful.
By the way the needle opening pressure of 240~255 bar sounds normal to me unless you are doing something special.
Which type of fuel did you use and how good the combustion condition inside cylinder was? If high viscous biodiesel B100 or high %biodiesel fuel is used, it is possible to clog up the nozzle tip. However, we did experiments on B10 used over 10,000 kilometers in the overhaul engine after 200,000 km used diesel pick-up truck; mechanical fuel pump, 4-hole nozzle injector with the injection pressure approx. 175 bars, smooth engine performance and better soot emission was achieved. No clogging at the fuel nozzle injector was found.
It is expected to happen in a Diesel DI engine because injector nozzle is exposed to the combustion process, thermal fluctuation and more precisely the quenching area of the combustion where chemical reaction is not complete.
The nature and formation of deposits in engines (including diesel injectors) and their effects on engine performance and emissions are complex and cannot be properly discussed in a short answer. Anyone interested could look up Chapter 3 of my book Fuel/Engine Interactions (SAE International, 2014).
Sir can you please share the link of the above mentioned page
Can u pls attach the file
Some more details about the book including the Table of Contents can be found at the following link
http://books.sae.org/r-409/
formation of injector deposits in diesel engines are due to the following parameters: nozzle tip temperature, existence of metals in fuel (zn effect is more than other metals) and injector assembling (sealing). among these parameters zn content is fuel is very important for formation of deposits, 0.3ppm Zn can reduce engine power to 10 percent due to coking.
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