In an engine, when the fuel remaining after normal combustion ignites explosively by high pressure and temperature produced from normal combustion,rather.

In an engine , when the fuel remaining after normal combustion ignites explosively by high pressure and temperature produced from normal combustion ,rather than spark from spark plug , it causes knocking or detonation.This explosive release of energy is what causes the characteristic "knocking”. It creates the characteristic metallic "pinging" Sound.

The main driver for knock is ignition timing. As the ignition is advanced - the spark is fired earlier in the engine operating cycle - the pressure and temperature during the combustion event become higher, thus making knock more likely.

Happens when fuel burn ignites irregularly and prematurely

Usage of fuel with low octane rating Poor design of engine and due to their own structural

problem

Under ideal conditions the common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion. The combustion is started by the spark plug allowing required time for the combustion process to develop peak pressure at the ideal time for maximum recovery of work from the expanding gases.

The pressure due to expanding gases in combustion chamber rises smoothly to a peak, as nearly all the available fuel is consumed, then pressure falls as the piston descends. Maximum cylinder pressure is achieved a few crankshaft degrees after the piston passes TDC, so that the increasing pressure can give the piston a hard push when its speed and mechanical advantage on the crank shaft gives the best recovery of force from the expanding gases.

When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat and pressure for a certain duration, detonation may occur. Detonation is mainly the instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A local shockwave is created around each pocket and the cylinder pressure may rise sharply beyond its design limits. If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed.

If the shockwaves created due to knocking have enough intensity

and/or over a long enough period of time , these shockwaves and excessive pressure and temperature can cause engine damage including (going from minimal to destructive).

Erosion and pitting of the piston and/or cylinder liners ,resulting in small wear particles which may enter the engine lubrication/oil system ,plug the catalysts, and/or possibly block valves from closing completely. The wear may not be unlike water pump cavitations' damage.

Actual holes punched or burned in the pistons.

Reducing air and coolant temperatures is always good for suppressing knock (colder air is also more dense, allowing the engine to take in a greater mass of air.)

The strategy for reducing knock - and so allowing more ignition advance (and hence more torque) - is to use a fuel with a higher octane rating. Higher octane fuels contain more components such as benzene that are resistant to self-ignition, and less of components such as n- heptane that self-ignite relatively easily.

There are two ways to meet the demand of modern high-performance engines for fuels of high octane numbers.

1. The first one is to produce artificial petrol that are rich in branched-chain alkanes.

2. Another method is to add an anti-knock agent to petrol. The most commonly added compound is tetraethyl lead [(CH3CH2)4Pb]. When burned, this lead compound produces small particles of lead oxide which tend to combine with the free radicals produced in the chain reaction of combustion. This slows down the reaction and makes it smoother.

To prevent lead from accumulating in the engine, 1,2-dibromoethane (CH2BrCH2Br) is added to petrol. The formation of lead bromide is volatile and is swept away in the car exhaust.

The exposure of lead in air leads to serious effect. Lead is a neurotoxin, or nerve poison. It can cause damage in the central nervous system (brain and nervous system), especially in young children.

The addition of tetra-ethyl-lead (TEL) a soluble salt added to gasoline was common until it was discontinued for reasons of toxic pollution.

Lead dust added to the intake charge will also reduce knock with various hydrocarbon fuels. Manganese compounds are also used to reduce knock with petrol fuel.

. Steam will suppress knock even though no added cooling is supplied.

Certain chemical changes must first occur for knock to happen, hence fuels with certain structures tend to knock easier than others. Branched chain paraffins tend to resist knock while straight chain paraffins knock easy.

Gasoline mixtures that are rich in straight-chain alkanes such as heptanes ignite very readily and explode rapidly. This causes 'knocking' and inefficient combustion.

Combustion of branch-chain alkanes like 2,2,4-trimethylpentane (iso -octane) is much smoother and more controlled.

Many countries are now phasing out the use of leaded petrol.

1. The production of unleaded petrol involves cracking, isomerisation and reforming reactions to generate high-octane petrol.

2. Unleaded petrol also contains an important additive methyl tertiary butyl ether (MTBE, octane rating 118).

Hence, gasoline mixtures rich in branch-chain alkanes are more efficient in burning and less likely to cause knocking

Fuels with high octane numbers burn smoothly and efficiently in high performance engines.

The isomerisation plant produces branching chain alkanes which improve the octane number of fuels.

We measure the problem using the octane number. The higher the number, the better the fuel. A fuel with a low octane number is likely to cause knocking. One with an octane number over 100 should be fine.

There are two main ways of increasing the octane number of petrol (i.e. improving it).

1. Use alkanes with branching chains rather than straight chains. 2. Use aromatic alkanes (with rings) These alkanes are produced on the site using the isomeriser and

the reformer,blended into the petrol at the end & is constantly monitored for its octane number.

Octane rating of a spark ignition engine fuel is a measure of the resistance to detonation or knocking compared to a mixture of iso -octane (2,2,4-tri methyl pentane, an isomer of octane) and n- heptane. It is a numerical representation of the antiknock properties of motor fuel, compared with a standard reference fuel, such as isooctane, which has an octane number of 100.

Octane rating does not relate to the energy content of the fuel .It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner.

1. RON (Research octne number) :- The most common type of octane rating used worldwide is the Research OctaneNumber (RON). RON is determined by running the fuel in a test engine with a variable compression under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

2. MON (Motor octane number) :- There is another type of octane rating, called Motor Octane Number (MON), which is a better measure of how the fuel behaves when under load as it is done at 900 rpm instead of the 600 rpm of the RON . MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance.

AKI (Anti-knock index) :- In most of the countries , RON is used. But in the United States , Canada and some other countries, the average of the RON and the MON is used, which is called the Anti-Knock Index (AKI). It may also sometimes be called the Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2.

Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. So, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. 

One of the strokes in engine working is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. So , The octane rating of gasoline actually tells you how much the fuel can be compressed before it spontaneously ignites by high compression and pressure. The amount of compression of air-fuel mixture is called the compression ratio of the engine i.e. the ratio of initial volume of gas-air mixture to the final volume of the same.

I conclude that compression ratio of your engine determines the octane rating of the gas or fuel you must use in the engine. A fuel with a higher octane rating can be run at a higher compression ratio without detonating. 

So, higher the compression ratio , more will be the energy output of the engine. That's why higher should be the octane rating so that fuel can resist more compression before ignition.

Now a days the scenario of fuel production & utilization has been undergoing a tremendous changeThe utility of fossil fuels has been increasing at a very high rate . The utility now a days is in such that the existing fuel resources doesn't serve for a much longer time. The time for which they will serve us are as shown

Resource Consumption(in MTOE)

% of total energy

Reserve (in MTOE)

Available for use(years)

Oil ,Liquid petroleum products

3507 35.7 1,51,984 43

Natural Gas 2122 21.2 1,56,706 74

Coal 2342 23.4 5,01,172 214

Total 7971 80.3 8,09,862

In addition to this even the flue gasses obtained by these fuels create lots of damage to the ecosystem. The systems that developed naturally over millions of years does take few days to get ruined . So we need to start a serious search for the alternatives to the existing fuels

Few things are to be kept in mind

(1) Cost of production & utilization

(2)  Eco friendliness

(3)  Efficiency of fuel produced

So we need to focus on Green fuels And find

What fuel can we use that will not completely destroy our atmosphere, and or environment ? The answer would be unanimously ------

The fuels that are likely to serve our purpose are : (1) Electric (2) Hybrid     (3) Natural gas (4) Hydrogen    (5) Fuel cells  (6) clean diesel (low sulfur)   (7) Biodiesel (B100)  (8) Ethanol (E85.)

Each of the mentioned fuels will be weighed out according to the amount of pollution they do and do not contribute to the atmosphere

The advantages of an electric ran vehicle can be summed up in four words “ PLUG IN AND GO ".Being that they are operated purely on battery, they give out no emissions or other toxins usually associated with modes of transportation. As far as being green and the lesser evil of most fuels, electric is the least damaging fuel to the environment.

ADVANTAGES :-

DISADVANTAGES:-Unlike a gas engine, it takes a lot longer to charge an electric car and it can be a hassle when making long road trips.For numerous reasons such as, not every gas station is equipped with compatible equipment to fuel electric cars, if your car stalls from a low battery it is harder to transport electric, than a gallon of gas.  In addition, the price of electric fueled vehicles is quite expensive and the price to convert your mobile can range from $5,000-$10,000. Not to mention your electric bill.

A hybrid is a VEHICLE  that uses two sources of fuel, some use gas combined with electric, solar or water.ADVANTAGES:- Since it is also using other sources of fuel it gives got less emissions than an engine solely using gasoline.  In addition, some hybrid cars you can get up to 50 per gallon.  This means on long drives or road trips you could drive well over 500 miles before you would need to stop and get gas.  

Hybrid cars are also very affordable where some are priced brand new from just $12,000 and up. 

DISADVANTAGES :- When a hybrid battery is drained or just stop working, it can cost around $5,000 to replace In addition, hybrids have a lighter body weight to compensate for its heavy engine where in case of accident it can be extremely dangerous for the driver

ADVANTAGES :- It burns clean as well as releases 70% less carbon dioxide than fossil fuel, making it a lot cleaner than traditional fuel.Natural gas has a higher heating value as well as is less expensive than traditional fuels.DISADVANTAGES :- It cannot be recycled, the world can only produce so much which in time natural resources can run out. In addition, the price to recover remaining natural gas due to flow, access etc, is expensive

 Hydrogen or water powered vehicles, even though they are not yet on the market, or even close to being completely developed as far as the other fuels mentioned in this report, hypothetically there would be many advantages. ADVANTAGES :- Emissions would be close to none, which is beneficial to our environment. Everyone would be able to afford  to fuel their vehicleDISADVANTAGES :-It has not been developed for mass production. In addition, unemployment would sky rocket due to no need for gas stations, or any other gas related  occupations. As well as we can only assume that, the purchase price of purely watered power vehicles would be very pricey.

A fuel cell is like a battery in a sense, but instead it combines hydrogen and oxygen to produce electricity.  Although it is a chemical process, it does not involve heat.ADVANTAGES :-It does not involve any moving parts, so traditional mechanical complications are minimal. Fuel cell emissions only emit water and it is very quite during operation.

DISADVANTAGES :- It is expensive to make as it relies on the use of platinum . Platinum even though already in use throughout the market is a natural resource and is bound to run out eventually, especially if we increase our dependency on using this rare metal.In addition, with changing technology mechanics will slowly find themselves out of a job as well as other vehicle maintenance services

Clean Diesel is diesel fuel put through a process where pressure is used to remove the majority of its sulfur content . It is also called as Ultra Low Sulfur Diesel (ULSD).ADVANTAGES :- It reduces 90% of emissions content, compared to traditional diesel energy.This promotes cleaner air as well as complies with EPA(Environmental Protection Agency) quality standards  and regulations. 

This type of fuel is also compatible with all diesel-fueled engines.

DISADVANTAGES :- The potential purchase price is more expensive as well as current availability is limited . In addition, this type of fuel is susceptible to eating through engine seals as well as during cold weather its liability decreases.

Biodiesel Fuel is diesel fuel consisting of oils derived from animal fat and recycled cooking grease.ADVANTAGES :- It can be made from home.  Most diesel engines can utilize biodiesel fuel as well as it emits less air pollutants and greenhouse gas.In addition, it is also biodegradable, non-toxic as well as is a lot safer to handle compared to traditional diesel.  DISADVANTAGES:-The disadvantages of biodiesel fuel is that B100 gets 10% less fuel economy then tradition diesel as well as it also not suitable for really cold weather conditions.

E85 or ethanol is a mixture consisting of 85% ethanol and 15% gasoline.ADVANTAGES :- E85 emits less air pollutants than traditional gasoline, also it is resistant to engine fuel mixture detonation or in laymen, “engine knock.”E85 is also not as expensive compared to  gasoline.DISADVANTAGES :-Only certain cars can run this fuel, such as flex-fuel cars, trucks, SUV’s. In addition, not every gas station carries E85, as well as your vehicle will have lower gas mileage and  as of now producing, the mixture is costly.

Relevant to the above explained contexts, scenarios and inferences it is evident that we can reduce engine knocking and its after effects using the green fuels. We conclude measures are to be taken at war foot lines to improve the quality of these fuels.