Petrol Technical Essay - 1st draft!
01-03-2006, 02:33 PM
#1
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Petrol Technical Essay - 1st draft!
Fuels
In this document I intend to answer some of the questions that keep cropping up from “Does SUL make my car faster” through to what is petrol and which grade should I use.
To start with I feel an introduction into the subjects of fuels is required, so I am going to start right at the beginning and cover the basics before getting on to the more complicated subjects.
Introduction – What is petrol?
This is a simple question which is difficult to answer, as each piece of information you find breeds another question.
Petrol is probably the best known of all the products from crude oil. Just under 20% of a barrel of crude oil goes to making petrol - the largest proportion for a single product.
Raw petrol (also called gasoline) is a mixture of hydrocarbons with between 4 and 12 carbons in their chains.
So raw petrol itself is not just one chemical, it is a mixture of several.
Some of these chemicals include:
Hexene (C6H14)
Benzene (C6H6)
Some of these are aromatics which are useful but very harmful.
The refining process is not perfect and some other chemicals find their way into the fuel. A good example of this is Sulphur which doesn’t work well with certain emissions treatment systems, hence the use of low-sulphur fuels.
But this is only half the story. You can’t buy raw petrol unless you are a supermarket or similar!
There are several other substances added to petrol in-order to do several different jobs:
Knock inhibitors – to resist detonation.
Anti-ageing – stability during transportation and storage.
Detergents – to clean the internals of your engine.
Corrosion Inhibitors – stops things rusting.
Icing protection – stops ice forming in the inlet.
Anti-foam – to improve tank filling.
Friction modifiers – to modify your oil!
These are referred to as the Additive Pack. So next lets look at each of these in turn and consider the impact they have on our engines.
Knock Inhibitors
This is the main factor the public are told about in terms of the quality of the fuel, but it is only one of the factors to consider.
Knock inhibitors improve the fuels anti-knock properties (octane rating). The higher the figure the greater the fuels resistance to detonation. There are two methods of measuring this:
RON – Research Octane Number
MON – Motor Octane Number
One point to make here is that in the UK we use RON. In the USA they take an average of RON and MON (ie RON+MON/2). So if you read an American book and they mention a petrol with what seems a very low octane rating (maybe 92) they aren’t using the same numbers we are!
So what’s the difference between MON and RON?
Well the way the work out the ratings of the fuel is very similar. Both use a single cylinder engine with a variable compression ratio. The fuel being tested is compared to two know fuels (n-heptane and iso-octane). These two fuels behave in opposite ways, one knocks easily the other resists knock VERY well. So by comparing a fuel (such as petrol) to these two known fuels a value is worked out.
The RON method uses acceleration as the main condition during testing (i.e. increasing engine speed). The MON method tests at higher engine speeds. Now here’s the crunch, high rpm to this type of engine is only 900 rpm!
Either way, the more octane, the better the fuel resist detonation. The way they do this is by raising the amount of energy that is required before the fuel will do anything (burn/react). So in fact this makes the fuel harder to burn, which is different to the perception that high octane fuels are more powerful.
Anti-ageing
This agent stop fuel going off. If you leave petrol long enough is becomes a sticky yellow gloop that will bung up everything. This is usually only a problem on vehicles that are left with fuel in them for many years!
Another point this raises is how long does fuel last. Fresh fuel is defiantly the best. The best most people will be able to do is to buy their fuel from a large petrol station that sells lots of fuel. The more they sell, the more often their deliveries they will have. This means the fuel you are buying has spent less time sitting in the underground storage tanks.
Over a period of week(s) the aromatic content of the fuel is the first to change as these are the most reactive. As this happens so the actual fuel changes (and often performs less well rather than better!).
Detergents
The purpose of detergents is to keep the inlet tract clean. This includes valves, ports, manifolds and throttle butterflies.
Its often thought that the detergents job is pointless. The opposite is true. On most engines the crank case emissions are pumped back round into the inlet system. Small amounts of oil mist can easily enter the inlet. On contact with hot surfaces (such as the back of the inlet valve) they can burn and form deposits. This reduces the air flow past the valve lowering the overall performance of the engine.
Corrosion Inhibitors
This basically stops metal components such as the tank itself from rusting. It is difficult to protect metal from rust with a substance that is not attacked by petrol. Luckily petrol does this for you.
Icing protection
If you’ve ever got petrol on your hands you will understand that evaporation has something to do with temperature. It take heat to make the petrol evaporate, so as petrol and cause a drop in the temperature of the air. If the air has a high moisture content, the water can freeze cause problems such as carburettor icing.
Anti-foam
As you move petrol about its natural tendency is to bubble. When your filling your tank you might notice this.
If allowed to certain conditions such as bumpy roads would make your fuel into a bubbly foam rather than a liquid fuel.
Fuel choice and use.
There are a large number of suppliers all claiming to have the best fuel.
To supply all the fuel in the UK there are several refineries. Each one of these is owned by an oil company. So for example Shell own the Shell Haven refinery in Essex. All the local BP stations will be filled at the Shell refinery.
The reason for this is that the base petrol is regulated very tightly and so is the same regardless of refinery. It’s the additive pack that changes from company to company.
Exceptions to this include Optimax (Shell might have changed this, but when launched this information was correct). This is(was) made at one refinery and then shipped out to all stores across the country.
Supermarket Fuel
Fuels destined for any supermarket is the same base fuel as any other petrol station. The reasons it is cheaper is that it will contain a cheaper additive pack and the fact that a supermarket buys its fuel in bulk!
Typically the fuel will not perform as well as a oil companies own brand, but like most things you get what you pay for!
What fuel should I use?
Simple. Use the fuel your engine has been designed to run on. If your car was designed to run on standard unleaded (95 RON) then use that. Using SUL will not make your engine more powerful as the engine will not take advantage of the fuels greater resistance to knock.
In more common vehicles (i.e. low performance!) high octane fuel can lower the performance and making cold starting difficult.
Alex
In this document I intend to answer some of the questions that keep cropping up from “Does SUL make my car faster” through to what is petrol and which grade should I use.
To start with I feel an introduction into the subjects of fuels is required, so I am going to start right at the beginning and cover the basics before getting on to the more complicated subjects.
Introduction – What is petrol?
This is a simple question which is difficult to answer, as each piece of information you find breeds another question.
Petrol is probably the best known of all the products from crude oil. Just under 20% of a barrel of crude oil goes to making petrol - the largest proportion for a single product.
Raw petrol (also called gasoline) is a mixture of hydrocarbons with between 4 and 12 carbons in their chains.
So raw petrol itself is not just one chemical, it is a mixture of several.
Some of these chemicals include:
Hexene (C6H14)
Benzene (C6H6)
Some of these are aromatics which are useful but very harmful.
The refining process is not perfect and some other chemicals find their way into the fuel. A good example of this is Sulphur which doesn’t work well with certain emissions treatment systems, hence the use of low-sulphur fuels.
But this is only half the story. You can’t buy raw petrol unless you are a supermarket or similar!
There are several other substances added to petrol in-order to do several different jobs:
Knock inhibitors – to resist detonation.
Anti-ageing – stability during transportation and storage.
Detergents – to clean the internals of your engine.
Corrosion Inhibitors – stops things rusting.
Icing protection – stops ice forming in the inlet.
Anti-foam – to improve tank filling.
Friction modifiers – to modify your oil!
These are referred to as the Additive Pack. So next lets look at each of these in turn and consider the impact they have on our engines.
Knock Inhibitors
This is the main factor the public are told about in terms of the quality of the fuel, but it is only one of the factors to consider.
Knock inhibitors improve the fuels anti-knock properties (octane rating). The higher the figure the greater the fuels resistance to detonation. There are two methods of measuring this:
RON – Research Octane Number
MON – Motor Octane Number
One point to make here is that in the UK we use RON. In the USA they take an average of RON and MON (ie RON+MON/2). So if you read an American book and they mention a petrol with what seems a very low octane rating (maybe 92) they aren’t using the same numbers we are!
So what’s the difference between MON and RON?
Well the way the work out the ratings of the fuel is very similar. Both use a single cylinder engine with a variable compression ratio. The fuel being tested is compared to two know fuels (n-heptane and iso-octane). These two fuels behave in opposite ways, one knocks easily the other resists knock VERY well. So by comparing a fuel (such as petrol) to these two known fuels a value is worked out.
The RON method uses acceleration as the main condition during testing (i.e. increasing engine speed). The MON method tests at higher engine speeds. Now here’s the crunch, high rpm to this type of engine is only 900 rpm!
Either way, the more octane, the better the fuel resist detonation. The way they do this is by raising the amount of energy that is required before the fuel will do anything (burn/react). So in fact this makes the fuel harder to burn, which is different to the perception that high octane fuels are more powerful.
Anti-ageing
This agent stop fuel going off. If you leave petrol long enough is becomes a sticky yellow gloop that will bung up everything. This is usually only a problem on vehicles that are left with fuel in them for many years!
Another point this raises is how long does fuel last. Fresh fuel is defiantly the best. The best most people will be able to do is to buy their fuel from a large petrol station that sells lots of fuel. The more they sell, the more often their deliveries they will have. This means the fuel you are buying has spent less time sitting in the underground storage tanks.
Over a period of week(s) the aromatic content of the fuel is the first to change as these are the most reactive. As this happens so the actual fuel changes (and often performs less well rather than better!).
Detergents
The purpose of detergents is to keep the inlet tract clean. This includes valves, ports, manifolds and throttle butterflies.
Its often thought that the detergents job is pointless. The opposite is true. On most engines the crank case emissions are pumped back round into the inlet system. Small amounts of oil mist can easily enter the inlet. On contact with hot surfaces (such as the back of the inlet valve) they can burn and form deposits. This reduces the air flow past the valve lowering the overall performance of the engine.
Corrosion Inhibitors
This basically stops metal components such as the tank itself from rusting. It is difficult to protect metal from rust with a substance that is not attacked by petrol. Luckily petrol does this for you.
Icing protection
If you’ve ever got petrol on your hands you will understand that evaporation has something to do with temperature. It take heat to make the petrol evaporate, so as petrol and cause a drop in the temperature of the air. If the air has a high moisture content, the water can freeze cause problems such as carburettor icing.
Anti-foam
As you move petrol about its natural tendency is to bubble. When your filling your tank you might notice this.
If allowed to certain conditions such as bumpy roads would make your fuel into a bubbly foam rather than a liquid fuel.
Fuel choice and use.
There are a large number of suppliers all claiming to have the best fuel.
To supply all the fuel in the UK there are several refineries. Each one of these is owned by an oil company. So for example Shell own the Shell Haven refinery in Essex. All the local BP stations will be filled at the Shell refinery.
The reason for this is that the base petrol is regulated very tightly and so is the same regardless of refinery. It’s the additive pack that changes from company to company.
Exceptions to this include Optimax (Shell might have changed this, but when launched this information was correct). This is(was) made at one refinery and then shipped out to all stores across the country.
Supermarket Fuel
Fuels destined for any supermarket is the same base fuel as any other petrol station. The reasons it is cheaper is that it will contain a cheaper additive pack and the fact that a supermarket buys its fuel in bulk!
Typically the fuel will not perform as well as a oil companies own brand, but like most things you get what you pay for!
What fuel should I use?
Simple. Use the fuel your engine has been designed to run on. If your car was designed to run on standard unleaded (95 RON) then use that. Using SUL will not make your engine more powerful as the engine will not take advantage of the fuels greater resistance to knock.
In more common vehicles (i.e. low performance!) high octane fuel can lower the performance and making cold starting difficult.
Alex
01-03-2006, 03:07 PM
#3
Nice info Alex.
Thanks for taking the time to type it out, shame Mike thinks its a pure cut and paste cause he is judging others by his own standards and cant write anything technical himself
Havent read it fully enough to ask any questions, but will do later probably
Thanks for taking the time to type it out, shame Mike thinks its a pure cut and paste cause he is judging others by his own standards and cant write anything technical himself
Havent read it fully enough to ask any questions, but will do later probably
01-03-2006, 03:09 PM
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Originally Posted by Mike Rainbird
Nice cut and paste .
.not one sentance is cut and paste...
Unless its from material I have already written myself...
must
resist
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its no go
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01-03-2006, 10:32 PM
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To supply all the fuel in the UK there are several refineries. Each one of these is owned by an oil company. So for example Shell own the Shell Haven refinery in Essex. All the local BP stations will be filled at the Shell refinery.
Great Post tho
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