write:It also varies as gasolines are formulated to provide optimum engine performance under different driving and climatic conditions. Individual constituents vary in ignition temperatu

diesel fuel. 9.2.1 Gasolines Gasoline or gasoline products are produced in crude oil refining. Due to different oil sources and refining procedures
gasoline products are complex mixtures of HC species that include paraffins
cycloparaffins
olefins
and aromatic HCs. Consequently
the composition of HC constituents varies from one refiner to another. It also varies as gasolines are formulated to provide optimum engine performance under different driving and climatic conditions. Individual constituents vary in ignition temperature and other combustion characteristics. Gasolines may contain small quantities of non-HC substances. These include normal constituents of petroleum such as P and S or contaminants introduced in the gasoline production process (such as H2O). Phosphorous and S reduce the effectiveness of catalytic converters; as such
additional refining steps are needed to reduce their levels. Water negatively affects engine performance. Gasolines may contain additives such as Pb
Mn
or oxygenates. The use of Pb in gasolines has been restricted in many countries to minimize damage to catalytic converters and safeguard public health. Nevertheless
it is still used in a number of developing countries. A Mn-containing compound
methylcyclopentadienyl manganese tricarbonyl (MMT)
is used in some countries as an octane booster. Refiners have promoted its octane-boosting potential and requested its approval in the U.S. Because of public health concerns
the USEPA has declined to approve its use. Oxygenates are used in the U.S. to boost gasoline octane ratings and decrease emissions of CO. 9.2.1.1 Octane Rating Gasolines are formulated to prevent knock
the noise transmitted through the engine structure when spontaneous ignition of the end-gas (fuel
air
residual gas) mixture occurs before the propagating flame. Such ignition produces high local pressures and pressure waves with substantial amplitude. Although knock can be severe enough to cause major engine damage
in most cases it is just an objectionable source of noise. The presence (or absence) of knock is a function of the antiknock quality of gasoline. A gasoline’s resistance to knock is defined by its octane number. The higher the octane number
the greater the knock resistance. The octane scale is based on two HCs
heptane and isooctane. The former has an octane rating of zero; the latter
100. Blends of these define the knock resistance of octane numbers between 0 and 100. The antiknock quality of gasolines is determined by two different methods. These produce what are called motor octane numbers (MONs) and research octane numbers (RONs). The antiknock quality of a gasoline is determined by averaging its MON and RON values. From 1923 until the advent of catalyst-equipped motor vehicles
Pb alkyls were added to gasoline to increase octane numbers. Their use allowed an increase in antiknock Control of motor vehicle emissions 331