The spontaneous automatic explosions in various parts inside the cylinder cause an unusual noise that can be caught by the sensors. There are several ways to prevent engines from knocking. Let us take a look at some of them in detail. Once the knock sensor receives the signal that knocking has started inside the cylinder, it sends the signal to the ECU.
The ECU commands the spark plug to retard the timing of the ignition. Therefore, the ignition takes place at a bit later stage and the high pressure and temperature are avoided. One must understand that all these functions take place in milliseconds due to electronic control. In this way, the combustion cycle continues and the knocking is gone with the self-correcting mechanism of the ECU. Should you remap your car? Well, the reason is here. The high octane fuel refers to the fuel which is more resistant to engine knock.
That means that it does not easily catch fire and high temperature and pressure. This is an extremely important property for petrol to have that it should get ignited only from the spark plug.
Using the knock-resisting fuel type will make sure that even if the ignition timing is advanced, the air-fuel mixture will not burn so easily. This technique is a bit counter-intuitive in that the compression ratio is directly proportional to the efficiency and performance of an internal combustion engine.
The higher the compression ratio, the more efficient the engine is and the better performance is the result. But higher compression ratio also makes the engine vulnerable to knock. That is the inherent characteristic of knock. That is why the role of ECU in determining the exact ignition timing across the entire range of engine operation is so important and difficult without electronic control.
The OEMs generally have the perfect balance of the ignition timing for a particular octane fuel where the engine performs well, is efficient and avoids running into engine knock. We know that the auto-ignition of the air-fuel mixture inside the cylinder takes place due to an increase in temperature. This means that proper cooling around the cylinder has to take place.
The walls of the cylinder should not remain hot otherwise the air-fuel mixture might get detonated as soon as it comes in contact with hot cylinder walls. Also, the intake air should be cool, which is generally done by the air cooler in bigger engines. Also read: What is Gasoline Direct Injection?
Why is it relevant in modern cars? The problem is that the popular components used to make the octane of a fuel higher slows the burn rate and a fuel with a burn rate that is too slow can result in an engine power loss. Of course, that is just typically what happens and it does not hold true for all fuels.
From this point, we would want to find a fuel that packs the most energy, has a compatible burn rate and has a vaporization characteristic that allows for peak performance. Racing fuels are essentially blends of anywhere from three to 50 components. There are different types of lettuce, olives, tomatoes and dressings.
A great salad is one that complements the engine combination being used. Your local gas station only offers E10 gasoline in three-different octane levels. Hence, not all octane racing gas formulations are going to deliver like performance. They will simply have similar resistance to knock as they share the same octane rating. Some fuel components add energy value to the fuel, some components are good burn accelerators and some components help vaporization. In general, energy values of different racing fuels are usually within three-to-five percent of each other.
The burn rate and vaporization characteristics vary from fuel to fuel. Burn rates need to be fast enough so that all of the air-fuel mixture can combust in the cylinder. If the burn rate of the fuel is too slow, energy will be lost through the exhaust valve. As engine rpm increases, the amount of time that is available for the burn to take place is reduced. In that sense, a fuel that works well in an engine that revs to RPM, may not be the best fuel in an engine that revs to 10, RPM.
As for vaporization, here is the ideal scenario: The fuel would enter the combustion chamber as a liquid. The reason you would want it in liquid form is that this would not displace any of the air that could potentially make its way into the cylinder. However, when the intake valve closes and the compression stroke gets under way, all of the fuel should change from a liquid to vapor state. With the fuel in a vapor state mixed with the air in the cylinder, the air-fuel mixture can be ignited and a high percentage of the charge will go from reactants to products.
Ethanol-blended fuels such as E65, E85 and E98 have become popular due to the availability at the pump in many regions of the country. E65 is usually found during the winter months in colder climates while E85 is the standard for the rest of the year.
E98 is usually only available by special order. The low-cost of E85 has made it a favorite among street enthusiasts living in areas that offer E85 at the pumps.
In many cases, the power and performance levels reached on E85 are on par with high-performance, leaded racing gasoline. However, there are considerations when using E Engines running on E85 are a bit cold-blooded and may have trouble starting at lower outside temps.
The entire fuel system must be compatible with E85 and the range available from a tank full of fuel will be reduced by about percent. The advantage of ethanol is that it does not have the corrosive issues that you find with methanol but it does have a lower energy content than methanol.
Methanol has been used as an alternative racing fuel to race gas for a number of years. One advantage of methanol is that it can be run very rich without a significant drop in power. This can allow the tuner to use the fuel as a cooling tool in the tuneup. The down side is that methanol can only pack about half of the energy found in gasoline. Fortunately, you can burn about twice the mass of methanol compared to gasoline with the same amount of air.
Depending on the vehicle, anything from zero to ten percent more power can be made with methanol over racing gasoline. Do not let this power gain fool you. There are significant drawbacks for the power gains. Pressure smoothly rises to a peak and after that, the exhaust valve opens and the piston moves up to eliminate the resulted burned gas.
It usually appears when a low octane rating or otherwise bad fuel is used. This convergence can also occur when the engine and fuel injection or carburetors are out of tune… or the most common cause occurs when deposits carbon build-up can be found in the cylinder. Thankfully again, carbon deposits can easily be eliminated… more on that, here. The two elements prevent the fuel from being burned efficiently and completely.
Detonation or Engine knocking tends to occur when the piston started the compression stroke and before the actual detonation time. It instantly creates a peak of cylinder pressure while the piston is also compressing these gases. For example, this can happen at the rate of at least times per minute when your engine is idling! Although this occurrence at idling is rare, an engine under load can have these stresses grow tenfold in short order.
Presence of these particles cause unnecessary wear and tear on other internal engine parts.
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