How octane cetane number can be used to determine efficiency of petrol diesel?

Answer 1

After oil change intervals, gasoline grades (Regular, Mid-Grade, and Premium) are about the most widely misinterpreted automotive concept -- and for good reason. When gas was still selling for a buck or so a gallon, ratings didn't receive that much press. At today's prices, however, there is a renewed interest and financial incentive in finding out which fuel is best to burn. Each gasoline grade is associated with an octane rating, which you'll see on those yellow stickers at the pump. In North America, regular gas is equivalent to an octane rating of 87; mid-grade with 89; and premium with 91. In some states, particularly those with a higher elevation, you may find what's sometimes called an "Economy" grade, which is lower than 87. At the other end of the spectrum, you'll often see premium gas with an octane rating as high as 95, depending on the gas company you get your fuel from. Why Octane Ratings? What purpose do octane ratings serve? In short, they measure the fuel's resistance to detonation, or the premature ignition of the fuel/air mixture during the engine's compression cycle. Marketing on the part of the oil companies and auto manufacturers has perpetuated the notion of octane ratings, which are classified by the Research Octane Number (RON) or the Motor Octane Number (MON). Both measure the fuel's resistance to detonation, but the MON measures the engine under load (i.e. towing) and so is roughly 10 points lower than the RON. RON is the measure found across Europe, while North America uses an average of RON and MON. This detonation is also known as "knocking" -- an annoying and, in the short term, largely harmless condition of reduced efficiency and power. The operative word here is "was," because with the adoption of modern fuel injection; engine knock sensors (generally after 1984); and unleaded fuels (1988), these timing/fuel related issues have essentially been alleviated in new vehicles. Some Gen Xer's will remember the Exxon Tiger anti-knock campaigns touting their premium fuel's ability to "Drive your engine clean." Today, though, fuel standards governed by the EPA, FTC and the state offices of weights and measures, require that all fuels -- including regular -- contain sufficient additives to prevent carbon buildup and protect your vehicle's engine, injectors, etc. Additionally, all gasolines (with the exception of E85 ethanol or other flex fuels) contain the same amount of latent energy, premium fuels simply have been "reformed" to have more compounds removed and/or additives added. Somewhat illogically, these additives actually make the fuel harder to burn, meaning they may help avoid the premature ignition in high compression and turbo/super charged engines. What's the Magic Number? The oil companies and refineries are a very influential bunch and have spent millions of dollars convincing both the automotive industry and consumer that there needs to be different "levels" (or qualities) of gasoline available for purchase. Car manufacturers have obliged by producing some high performance/high compression engines that require higher octane fuel to achieve their highest marketed horsepower ratings. In other words, you can't get that 255 horsepower you see advertised on TV without Premium fuel. Meanwhile, the oil companies figure they can use this "need" for Premium fuel as an excuse to peddle it to anybody who will pay. The fact is, though, that Premium fuel isn't necessarily the most efficient for even that "255 horsepower" car. So what's the magic number? The absolute best advice when considering which fuel to use is to consult your owner's manual. The manufacturer has designed the engine to perform optimally with a specific fuel rating in mind, which will provide the maximum efficiency and power. Can you use mid-grade or premium fuel in your engine, which is rated for regular? Yes, but it will be a waste of money. Even though the oil companies might try to make you believe otherwise, your car will not run cleaner, more efficiently or produce any additional power. Can you use regular gas in your vehicle even though the manufacturer specifies mid-grade or premium? Yes, you can but your engine will not perform in its most efficient range and over a prolonged period, you risk the possibility of engine damage. The additional few bucks you spend per tank-full will likely outweigh the money you save by running a fuel that provides less fuel efficiency. Also some manufacturers have even tried to void warranties in claims where evidence shows that improper fuel was used. One consolation is that at today's prices, the margin of premium over regular has fallen, meaning it is cheaper in relative terms to opt for the premium. Knock, Knock: When to Deviate from the Manufacturer's Claim When to "upgrade" If your fuel-injected vehicle is experiencing detonation (knocking), it may be a sign of some mechanical problem like faulty spark, carbon build-up, tainted gas, etc… If you or your mechanic has explored all these possibilities however, and you still have the problem, you may want to try bumping up a grade. This may happen with high mileage cars or during considerable periods of load, like towing, for example. When to "downgrade" Just because fuel prices have ballooned to four bucks a gallon is still no reason to automatically default to regular fuel. However, due to the additional additives found in premium grades, you may occasionally experience difficulty starting your engine, particularly during the winter months. An especially cold engine (i.e. winter) doesn't contain enough heat to immediately ignite this fuel, at least until it has warmed up some. If you experience rough starting or feelings/sounds that your engine is not running on all cylinders during and just after cold month startups, you may want to consider regular fuel while the snow flies and switching back to the "good" stuff in the spring.