Defects in the mechanical part of the engine do not appear by themselves. Faulty fuel equipment in diesel engines can lead to burnt pistons and other unpleasant consequences.
The piston is one of the main elements of the internal combustion engine. In a diesel engine, the piston operates under high thermal loads, high pressure, friction, etc. The slightest problem of a mechanical or thermal nature inevitably leads to a breakdown.
A common problem is cylinder knocking and blue smoke. Defective piston rings cause oil to enter the combustion chamber. The result is piston burnout. Also, pistons often burn out due to a “pouring” nozzle. The injector sticks open and fuel flows throughout the entire combustion cycle. Often the piston burns out due to uneven heat distribution. A faulty oil jet (piston cooling jet) or a problem with the water cooling will cause the piston to overheat and burn out.
Many factors can converge at the same time. Clearances, huge pressure in the cylinder, uneven heat distribution, fuel quality, injector performance, etc. ultimately lead to engine failure in general, and in particular to burnout of the piston.
Possible causes of piston burnout:
- faulty injectors;
- defects in the fuel pump;
- the amount of injected fuel and the injection moment are not adjusted;
- insufficient compression, incorrect valve timing, leaking valves;
- oil in the combustion chamber (more often due to faulty piston rings);
- low cetane number of diesel fuel;
- insufficient amount of lubricant;
- piston cooling failure.
The study of various piston damage shows that all causes of defects and breakdowns are divided into 4 groups:
- cooling interruptions
- lubricant imperfection
- unreasonably large thermal and force influence from the gases in the combustion chamber
- mechanical problems.
At the same time, many causes of piston defects are interrelated, as are the functions performed by its various elements. In particular, defects in the sealing belt cause piston overheating, damage to the fire and guide belts, and scuffing on the guide belt leads to a violation of the sealing and heat transfer properties of the piston rings.
Ultimately, this will most likely provoke burnout of the fire belt.
Why did the piston burn out
Poor combustible mixture
For 1 liter of gasoline, it contains more than 16 kg of oxygen. It doesn't burn very fast. the motor is overheating, energy drops, as a result, the entire engine overheats. The piston in this list is key, because it is aluminum (except for tuned pistons) and is located directly in the fuel combustion zone. As is well known, aluminum melts at about 660 ° C, and when to think about what maximum allowable engine temperature only 150 degrees, and then 200 ° C no longer lubricates any oil, then it does not take long to calculate that a poor mixture is still capable of heating up parts in the middle of the motor more than 4 times more.
Bad gasoline
Body gasoline burns through the piston for the same reason - as a result of overheating. Because the gasoline that we pour into our gas tank often cannot be called gasoline. Proper gasoline burns at a sufficiently low temperature, while expanding very strongly, because the essence of any gas driven to top dead center ( TDC), lies in the fact that it expands to the maximum relative to its original volume, thereby extremely convincingly pushing the piston down, and combustion and the generated temperature are all side effects, without which the engine would be fine. In bad gasoline, as in normal, there are components such as benzene, gasoline and other bad substances. The fact is that they are contained in low-quality “gasolines” in absolutely different proportions, but in fact in larger proportions than standards allow.
Burnt piston signs and symptoms
These two wonderful components burn, releasing more heat and at the same time have a small expansion factor during combustion, and at the same time, being part of gasoline, they slow down the rate of combustion, reducing power. Therefore, when driving on such fuel, in order to achieve proper traction, it is required to twist the throttle stick more than when driving on normal gasoline, but here's the misfortune: we get the necessary traction complete with a much higher combustion temperature and excessive fuel consumption, and the result of this is a hole in piston.
Many factors affect the operation of the piston and it is impossible to give an unequivocal answer whether a particular piston will burn out or some other defect will occur. You can estimate the probability of an event occurring. And in order to prevent the onset of such an unpleasant event as piston burnout you must follow the rules written in the RE. After all, piston burnout is a purely operational defect.
The zone of the bottom and the top zone is completely destroyed. The hot zone burned out to the reinforcing insert. The molten piston material has moved along the piston skirt and caused damage and scuffing there as well. The reinforcing insert of the first compression ring is partially preserved only on the left side of the piston.
The rest of the reinforcing insert detached from the piston during operation and caused other damage in the combustion chamber. Parts of the piston flew off with such force that they fell through the intake valve into the intake manifold and thus also into the adjacent cylinder and caused damage there (impact marks).
to fig. 2: in the direction of injection by one or more jets of nozzles, erosive burnouts appeared on the piston bottom and on the edge of the heat zone. The piston skirt and piston ring area are free of burrs.
Damage assessment
Damage of this kind occurs especially in direct injection diesel engines. This applies to pre-chamber diesel engines only if one of the pre-chambers is damaged and, as a result, the pre-chamber engine turns into a direct injection engine.
If the injector of the corresponding cylinder does not maintain injection pressure after the end of the injection process and the pressure drops, vibrations in the high pressure fuel line can once again raise the injector needle, so that after the end of the injection process, fuel is injected again into the combustion chamber (mechanical injectors).
If the oxygen in the combustion chamber is exhausted, then individual drops of fuel flow through the entire combustion chamber and fall on the bottom of the piston moving down closer to the edge. They quickly burn out there with a lack of oxygen, and quite a lot of heat is generated. At the same time, the material in these places softens. The dynamic forces and erosion of the fast-flowing combustion gases pull out individual particles from the surface or remove the head completely, resulting in damage.
Possible causes of damage
- Leaky nozzles or hard moving or stuck nozzle needles.
- broken or weakened injector springs.
- defective pressure reducing valves in the high pressure fuel pump injection quantity and injection timing not adjusted according to the engine manufacturer's instructions.
- in prechamber engines: a defect in the prechamber, but only in combination with one of the above reasons.
- ignition delay due to insufficient compression as a result of too much clearance, incorrect valve timing or leaking valves
- too long delay due to non-flammable diesel fuel (too low cetane number)
A diesel engine has significant differences from a gasoline engine. Engines differ in particular by the principle of ignition, for gasoline from a spark, for diesel from compression. Accordingly, the load on the pistons themselves also exceeds gasoline counterparts by 3 times. The compression of a gasoline engine reaches a value of 10 bar pressure. In turn, the diesel engine provides a pressure of 30 bar. The compression ratio is also 3 times higher.
But, at the same time, the diesel engine is more wear-resistant. True, there are a number of nuances that make a diesel engine less stable than a gasoline one. Most often, a diesel engine will serve its owner longer if everything in the engine is good and it is serviced on time. But, practice shows that it is not good in 90% of cases.
3 main reasons why burnt diesel engine piston
What causes a diesel engine piston to burn out? The first and most likely reason is that the nozzle is pouring. Simply put, it delivers more fuel than is allowed by the manufacturer. As a result, one has to work with a greater volume of combustion and flame than is allowed. This procedure is accompanied by a characteristic "tah-kam" sound.
If you use the machine for a long time in this mode, then over time the walls of the piston will melt. Moreover, the problem will manifest itself at the first melting of the pistons. The molten aluminum material will fly off the walls and accelerate the destruction of the engine. The longer you drive like this, the more parts in the engine you will need to replace. Until the overhaul Or a complete engine replacement.
This happens because pieces of abrasive get between the sleeve and the piston, erase the surface, create scoring. Injectors and their incorrect fuel supply are most often to blame for this.
Also, oil can be the cause of burnout of the pistons. Such cases also appear quite often. This can happen because the valve guides of the cylinder head could loosen up and the seals could lose their stability. Oil flows down the intake valve and slowly drips onto the engine piston. The combustion temperature of the oil is higher than the temperature of the fuel. And this situation causes the engine to gradually die.
It happens that antifreeze enters the combustion chamber of the piston. The ingress of water or antifreeze into the combustion chamber catalyzes the explosion.
How to deal with the problem?
It is very easy to avoid this situation. Go through the technical inspection of the car in time, in case of any misunderstanding and unnecessary sounds in the engine area, be sure to check the car at the service station. In addition, constantly monitor the level of oil and antifreeze in your car. Timely engine diagnostics warns of a malfunction.
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Each piston in your vehicle's engine has two separate compression rings on the piston head and an oil scraper ring assembly on the piston skirt. The rings roll in the annular grooves inside the piston. Compression rings contain pressure from expanding gases inside the combustion chamber, helping to utilize the energy generated while preventing blow-by gases from entering the crankcase. The oil scraper scrapes excess oil from the cylinder walls ahead of the compression rings to prevent oil from entering the combustion chamber. Failure of any of these rings will result in loss of performance if there are other problems and symptoms.
Broken compression rings
The result of broken compression rings will immediately reveal itself in the form of loss of power, rough idle and possibly malfunction of the damaged cylinder. Insufficient flue gas containment will cause blow-by gases to enter the engine crankcase and be forced out through the crankcase ventilation system. The crankcase ventilation valve is most likely located on the valve cover. Disconnect the exhaust tube from the crankcase ventilation valve, and if you notice a strong smell or smoke coming out of the valve, then there is a good chance that the compression rings are broken.
In addition to the obvious problems in engine performance, other problems can develop over time. For example, a diesel engine running on high sulfur marine or agricultural fuels can be severely damaged due to loss of compression. Partially burned fuel hits the rings, and the sulfur in the fuel mixes with the water present in the oil, resulting in a chemical reaction that turns into sulfuric acid, which damages the internal components of the engine.
In gasoline engines, the fuel acts as a solvent, thinning the oil and helping protect internal parts. Check compression with a tester. Typically, compression should be around 11-12 bar with no more than 15% difference between cylinders. If the compression on one of the cylinders is less than these values, then most likely the ring is broken on it.
Broken oil ring
A broken oil scraper ring assembly can be recognized by the quality of the exhaust gases, which turn blue in color and have a distinct oil smell. Exhaust gases are emitted in the form of puffs of blue smoke during the cycle of operation of a damaged cylinder, and exhaust of a normal type is emitted in the cycle of operation of serviceable cylinders. These jerky puffs allow easy visual diagnosis. Other symptoms include oil loss in the absence of leaks, as well as oil deposits on the spark plug of an inoperative cylinder.
Mechanical damage
In addition to the damage caused by blow-by gases, improper lubrication and free hydrocarbons contained in the oil, there are obvious mechanical damages. The edges of the rings can push against the cylinder walls, preventing other rings from making good contact with the cylinder walls, and exacerbate symptoms. The annular groove in the piston can be damaged, and since the cylinder walls and rings are harder than an aluminum piston, the piston itself can be damaged or partially destroyed, resulting in more serious damage.
Since any particles settle on the bottom of the engine crankcase, causing possible more damage, broken rings should be replaced immediately. You can remove the cylinder block cover to inspect damaged cylinder walls, or use a mechanical chamber passed through the spark plug hole. This will be the least invasive procedure.
Causes of broken rings
Since the rings were properly sized and installed during engine assembly, any damage to the rings was likely caused by other mechanical problems. When the engine overheats, the piston expands, reducing the gap between the piston and the cylinder. This reduced clearance can lead to metal transfer from the piston to the cylinder, or so-called galling.
Carried aluminum can collect on the cylinder wall and cause leakage or breakage of the top compression ring. Oil scraper rings can break if there is an increased gap between the piston and the cylinder, causing too much piston popping. The piston skirt (and in fact the cylinder machines themselves) can be damaged, and this, in turn, can destroy the oil scraper ring assembly.
