The competition between the intended controlled and unintended spontaneous combustion causes the energy from the burning fuel to disperse unevenly, which can cause damage and place high pressure on the engine's piston before it enters the power stroke the part of the cycle when the piston's motion is generating power.
Before electric computerized ignition was widely used, this knocking commonly occurred and could cause significant engine damage. Most modern engines have sensors to detect knocking.
When detected, the computer delays the initial spark, which causes the controlled combustion to take place at a point when compression is not at its highest point. Although this eliminates the knock, it can cause the engine to run less efficiently. A similar undesirable condition is called pre-ignition, when the fuel ignites on its own before the spark ignites it.
Modern engine computers minimize this condition by controlling the timing of valves and fuel injection; however, this control mechanism can also come with a fuel-efficiency or emissions penalty. The standard means of testing octane is with an octane testing engine. This test is similar to the way the mass of an object can be determined by comparing it to objects references of known mass on a balance scale.
Primary Reference Fuels PRF of precisely known octane are formed by combining iso-octane, heptane, and other well-known standards such as toluene. These PRFs are used to bracket a given fuel sample to determine the pressure at which similar knock intensities are observed. To determine the RON, the fuel is tested under engine idle conditions with a low air temperature and slow engine speed.
To determine the MON the fuel is tested under the more stressful conditions of higher air temperature and engine speed. Current designs see image below allow the same engine to perform both tests. Despite this flexibility, many testers still prefer to use more than one machine with each specifically set up and calibrated to perform either RON or MON tests.
Gasoline explained. What is energy? Units and calculators. Use of energy. Energy and the environment. Also in What is energy? Forms of energy Sources of energy Laws of energy. Also in Units and calculators explained Units and calculators Energy conversion calculators British thermal units Btu Degree days. Also in U. These options include increasing the compression ratio, changing the timing of spark ignition, injecting less fuel into the cylinder, and more. Additionally, engines designed to work with higher octane also burn the fuel more completely — meaning less harmful emissions in exhaust.
One MIT study even estimated that if higher octane fuels and engines designed for them became more widespread, the U. With that knowledge in hand, we can now come back to those numbers — 87, 89, and Or put another way, an octane rating of 87 or higher can withstand the compression ratios used in most cars.
Anything lower and you risk engine damaging pre-ignition or knocking — processes that occur when the compression ratio generates more pressure and heat than the fuel can handle, causing it to combust early and push down against the piston while it is still moving upward in Step 2. And since 87 is the standard octane rating for the fuel most engines use today, the 89 and 93 octane rated fuels are only different because they can handle more heat and pressure before igniting on their own.
This, in turn, means they can run in performance engines designed to use higher compression ratios. And there you have it. Octane is simply a measure of how much heat and pressure a fuel can withstand before exploding, and — in tandem with a properly designed engine — a higher octane fuel can increase performance and efficiency while decreasing emissions.
Wonderful site you have here but I was wanting to know if you knew of any community forums that cover the same topics talked about here? If you have any suggestions, please let me know. Great article! Really appreciate for your response! Hi Daniel, Thanks for the response! What type of vehicle do you have? It only makes sense to switch to premium if you have a vehicle that can take advantage of the higher octane. No worries! Hope that helps—have a good one. What octane ratings really mean for your car By: Akhtar Hussain Director of Refined Fuels Marketing, Refined Fuels in Fuel Efficiency Load up the snacks and crank up the tunes, because summer road trip season is officially here.
Summer trips mean long hours on the road hauling heavy gear. Towing loads like boats and campers can be especially taxing on the family car.
Fuel grades like regular, plus and premium are dictated by their octane rating. So what do those different octane ratings at the pump really mean?
Why octane ratings matter for your engine Gasoline-powered motors work by igniting a mixture of air and fuel at carefully timed intervals with a spark plug.
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