The two most important characteristics of petrol are its instability and octane ranking (that is its resistance to self-ignition). Volatility is uttered in terms of amount percentage explicitly distill at or below fixed temperatures. If petrol is too volatile, when it is used at high ambient temperatures, the petrol is liable to vapourise in the fuel lines of carburetted engines, and type vapour locks. Petrol for an IC’ engine has boiling point series as of about 311 k to 477 k.
The volatility of petrol affects ease of initial, length of warming up stage and engine routine during normal process. Petrol must, hence, remain a liquid until it enters air stream in mixing chamber of carburettor to form fuel—air mixture. At this time, it must rapidly vapourise and mix equally by the air in proper proportions.
Too elevated percentage of fuel volatility causes vapour lock in fuel line, fuel pump and carburettor. As an effect of vapour lock, the fuel supply to engine abruptly stops the engine. 1. Ainti-knock values of petrol The tendency towards explosion is over come with addition definite compounds for example tetraethyl lead in petrol. The capability of fuel to oppose detonation is calculated by octane rating. Octane rating of a fuel is determined through matching it by mixtures of normal heptane and iso-octane in a test engine. The octane ranking is in octane number and is identified as ‘ONR’. A fuel of low octane number knocks simply, while a high octane value petrol in extremely resistant to knock. 2. Additives in Petrol
- Metal deactivators are defensive the petrol as of the risky effects of definite metals that mix up in oil refinining method in fuel system and vehicles.
- Phosphorous compounds which combat surface ignition and foating of spark plugs.
- Oxidation inhibitors are preventing the creation of gum as the petrol is in storage.
- Detergents are extra to keep the carburettor all the time clean.
- Rust resistors which defend the fuel system of vehicles.
- Dye which provide colour to fuel for identification.
- Ice-resistors which protect carburettor iceing and freezing of fuel line.