In the process of operation of the internal combustion engine, as is clear from the name, the fuel is ignited and burns. But this is not a chaotic process, but precisely controlled. And when it goes astray, the engine makes extraneous sounds. The most critical is the metallic “ringing” characteristic of detonation. We tell you what detonation in a car engine is and why you should not ignore it.
What is detonation in a car engine
In an internal combustion engine, ignition of the fuel-air mixture in the cylinder occurs at a strictly defined moment of time, when there is a necessary portion of air in the combustion chamber, a corresponding amount of fuel is added, the piston compresses the resulting mixture and the spark plug is triggered.
Further the mixture burns – the combustion front spreads from the spark plug electrode uniformly in all directions with subsonic speed. Due to this, the temperature and pressure in the combustion chamber increases, relatively smoothly and without sudden jumps. This is the normal mode of the engine, in which it can operate for a very long time.
But sometimes there is detonation in the engine, but what it is – not all car owners understand. In fact, gasoline detonation is not combustion, but its explosion, almost instantaneous. As a result, a wave is formed, a pressure surge, spreading through the combustion chamber at supersonic speed. Reflecting off the walls, it causes a metallic sound, about which they say: “fingers knock”. Though in fact piston fingers have no direct relation to what is happening.
The efficiency of the motor drops sharply, while the loads, on the contrary, increase. As well as the temperature of the parts surrounding the combustion chamber. In cases of quite extreme detonation, the engine can fail after only a few minutes of such operation.
Modern engines are able to fight detonation on their own. For this purpose, special sensors are used, which are installed on the cylinder block. By their principle of operation, they are close to microphones, that is, they hear the very “finger knock” and feel the vibrations caused by detonation.
The sensor (or sensors) transmit commands to the electronic engine control unit, and the latter corrects the ignition advance angle to eliminate detonation. The optimum ignition advance angle is selected based on the octane rating of the fuel used, the current engine load, and the conditions under which detonation occurs.
It is important not to confuse detonation with two other phenomena. The first is the so-called caliche ignition, which appears when the engine is running for a long time in the heat, with a high load and on low-quality gasoline. In this case, glowing parts in the combustion chamber provoke spontaneous ignition of fuel without a spark – as a rule, the hottest is the electrode of the plug itself. This problem is cured by installing more suitable “cold” plugs with a high caliber number. However, with strong detonation, the entire combustion chamber heats up – and caliche ignition may continue even when explosive combustion has stopped.
The second is the “dithering” characteristic of carbureted engines. This is the name of fuel self-ignition after the ignition is turned off at low crankshaft speed. At this point, air almost ceases to enter the combustion chamber, the temperature in it increases – and this again provokes caliche ignition. But here it lasts only 2-3 seconds, so it does not cause critical damage.
How to recognize engine detonation
The most obvious symptom indicating the appearance of detonation is a characteristic metallic knock from under the hood, quite ringing and often repeated. The sound of engine detonation is difficult to confuse with others: imagine that someone hits the cylinder block with a metal object. Actually, this is how the shock wave manifests itself, which occurs in the combustion chamber and is transmitted to its walls, and they already “report” the problem to the outside. Often the knock is accompanied by increased vibrations, they are also attributed to the characteristic signs of engine detonation. However, in modern cars detonation can be quite difficult to distinguish from the cabin: noise insulation of the cabin and the engine itself has become better. So you have to listen. Through the music from the stereo “finger knocking” may not penetrate.
It is worth to pay attention to problems with engine starting, increased fuel consumption and power reduction, which in turn can manifest itself as a failure of traction under load and general deterioration of acceleration dynamics. It is clear that such phenomena may indicate other engine malfunctions, but if all this is accompanied by metallic clanking from under the hood, the problem is obvious.
What is the danger of engine detonation
When the engine detonates, mechanical and thermal loads grow simultaneously, and they act on almost all parts. Pistons are the first to be hit – they literally crumble from pressure surges and break out piston ring partitions. At the same time, the valves, whose plates cannot withstand high heat, suffer. The cylinder head gasket burns through, connecting rod liners wear out quickly, and in especially neglected cases even the cylinder block or the cylinder head may require repair.
In this mode, a few minutes of operation of the power unit is enough to ensure its failure, and the owner of the car – expensive repairs. Modern engines made of light alloys are particularly vulnerable to detonation, as they are unable to withstand pressures and temperatures that exceed several times the standards. It may even happen that because of the caliber ignition crank mechanism spins in the opposite direction to the working direction – and the motor will definitely have to be repaired.
Main causes of detonation
There are not so many causes of detonation, so you can understand without the help of specialists what causes detonation in the engine of your car. Here are the main options.
Fuel with unsuitable octane number
The most common cause of internal combustion engine detonation. Each engine is designed for a certain type of fuel, taking into account the parameters of which sets the compression ratio. That is why the minimum permissible octane number of gasoline, which is suitable for refueling, is necessarily indicated on the fuel tank hatch cover. If unsuitable or substandard fuel is poured into the tank, it simply cannot burn properly with the compression of the fuel mixture inherent in the engine design. In modern cars electronics is able to adjust the engine to such gasoline, but only within certain limits. And at the same time, its power will still drop, and the engine temperature will slightly increase. Usually such detonation manifests itself after refueling.
Ignition problems
Detonation can also be provoked by off-set ignition settings. Too large an advance angle will lead to the fact that the spark will appear before the piston comes to the top dead center, which means that the ignition of the fuel-air mixture will occur before it is distributed in the combustion chamber. Similar problems will occur if improper spark plugs are installed.
Irregular fuel mixture composition
Detonation at idle speed usually does not occur: the loads are too low. More often detonation of the engine is felt during acceleration, when the fuel-to-air ratio in the cylinders is especially critical. Too poor a mixture (a lot of air, little gasoline) increases the temperature of the exhaust gases and, in fact, the combustion chamber. That provokes explosive combustion.
Another source of problems can be the ingress of too much engine oil into the combustion chamber, which reduces the detonation resistance of the fuel-air mixture.
Cylinder fouling
If deposits have accumulated in the engine cylinders, they provoke detonation. Firstly, deposits on the inner surface of the combustion chamber reduce its volume and thereby increase the compression ratio. So even fuel with the right octane rating is ignited incorrectly. Secondly, deposits impair cylinder cooling, and in the process of engine operation they become so hot that they ignite the fuel mixture before it is ignited by the spark of the spark plug. If you’re experiencing glow plug ignition, it’s probably due to fouling, too.
Cooling system failure
When detonation shows itself on acceleration, it’s a sure sign of problems with the engine’s cooling system. The engine overheats, the combustion chamber heats up, and the fuel-air mixture burns unpredictably. The reasons for engine detonation under load should be looked for in the cooling system.
How to eliminate engine detonation
Each cause of engine detonation requires its own solution, but in general we are talking about not the most complicated and fairly obvious ways to eliminate problems.
Quality fuel
In a situation where detonation is provoked by gasoline with a low octane number, it’s easy enough to choose proven gas stations that guarantee quality fuel. If you do fill up with substandard fuel and there is no possibility to drain it from the tank, you can use an additive with octane corrector, which will allow you to get to the source of quality gasoline with minimal losses. At a minimum, it is worth diluting the fuel in the tank with the highest octane gasoline possible.
Factory ignition settings and suitable plugs
In this case, there is only one thing to recommend: go to a service to check the ignition angle and, if necessary, return it to the factory settings. The same goes for the plugs: make sure they are in good working order and meet the car manufacturer’s requirements, and if not, replace them with suitable ones.
Regular load on the engine
We advise you not to drive exclusively at low speeds and do not be afraid to occasionally crank the engine to high speeds. At these speeds, the carbon deposits accumulated during jostling in traffic jams heat up and burn out – thus the engine effectively cleans itself. When massive deposits inside are suspected, a cracking procedure can be used.
Check the coolant level and system serviceability
If detonation is provoked by engine overheating, the first thing to do is to check the coolant level. If its level is normal, it is necessary to make sure that the thermostat and fan work correctly, flush the radiator. Usually this is enough.
Brief information
- Detonation is the process of explosive ignition of the fuel-air mixture in the combustion chamber of the engine.
- Detonation of the engine manifests itself first of all by a characteristic metallic “ringing”.
- Detonation of the engine is fraught with its breakdowns due to increased mechanical and thermal loads.
- The main causes of engine detonation are unsuitable (low-quality or non-compliant with the manufacturer’s requirements) fuel, incorrect ignition system settings, internal contamination of the cylinders, malfunctions with the cooling system.