Most cars take regular. Others require premium. Your wallet might thank you. Regular gas is rated at 87 octane in most states, while premium gas is often rated higher at 91 or Fuel with a higher octane rating can stand up to higher compression before it detonates. Essentially, the higher the octane rating, the lower the likelihood that detonation happens at the wrong time.
On occasion, this occurrence will likely not harm your vehicle. However, if it happens frequently it may quicken the decline of your engine's performance. Engines with high compression ratios or turbochargers often require high octane fuel found in premium gas for optimal performance and fuel efficiency.
However, the majority of cars on the road today are optimized to run on regular gas. It allows performance-oriented engines specifically, those with higher compression ratios to burn gasoline at higher pressures and higher temperatures.
Octane rating is a measure of grace under pressure: how evenly a gasoline will burn under difficult conditions, like hard acceleration. Gasoline with a higher octane rating does not self-ignite easily, and burns more evenly than lower-octane fuel under harsh conditions, resisting detonation and knocking. Modern engines, with electronic sensors and controls, are very good at preventing detonation of lower-octane gas this is why drivers no longer hear much knocking.
But high-octane fuel is still specified when designers want to achieve better acceleration and power output, and when they are willing to accept a slightly bulkier and heavier engine with higher operating costs. Related Questions Is fire a solid, a liquid, or a gas? Is there a way to check a building for structural damage without knocking down walls?
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.
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