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Petrol

What's in petrol - Interesting Article!

This is something different but well worth reading. It was written by our learned friend in Stoke and we think is of interest to any car or bike owner.

Well…………! In The Beginning there was Carbon and Hydrogen.

These got together in accordance with rules forged in the Big Bang (yes, really!) to make methane, one carbon atom with 4 hydrogens stuck on.

A bit later, (only 4000 million years) other atoms started getting together and finally came up with Life, a self-reproducing chemical mix. The reproducing bit was quite fun, but after 600 million years even that gets boring.

So, a more or less intelligent life-form invented The Car and the Motorcycle, the ultimate boredom cure. This was, and is, powered by the Internal Combustion Engine, which must have fuel.

Methane is a fuel, which means it burns in air to produce energy, but unfortunately it’s a gas; a tank-full would propel a Honda 50 for about half a mile.

But! Methane had not been idle since the formation of planet Earth, and had joined up with more carbons and hydrogens to make chains called ‘hydrocarbons’. Well, they weren’t called that at the time. They had to wait for a life-form to evolve that liked giving things names, and a hundred and 20-odd years ago chemists had to learn Latin, so they called the one with five carbons ‘pentane’, the 6-carbon one ‘hexane’, then ‘heptane’ then ….wait for it…. the 8-carbon one ‘octane’ and so on. (If we were naming them now the last one would be called ‘eightane’ so you would need 95 minimum REN for your engine.)

All these things were liquids, very thin and volatile, and pure concentrated energy. The Hildebrand and Wolfmuller (rough 1894 equivalent of the Honda 50) now did 100 miles to the tank full.

Unlike water, these liquids don’t stand around in lakes. They are hidden underground in porous rock so you have to drill for them. The old name was ‘petroleum’ meaning ‘rock oil’ but this was soon shortened to ‘petrol’. The petrol came out of the wells mixed with heavy oil, so it had to be distilled off in an oil refinery.

Early on, the pale coloured stuff that evaporated easily and caught fire very easily was sold as internal combustion engine fuel. It was a simple as that. ‘Octane Number’ hadn’t been invented, but in modern terms this ‘light petroleum fraction’ was about 50 Octane. Now we all know that in the GCSE Science engine The Piston squeezes the air/fuel mixture, then The Spark Plug ignites it to produce The Power Stroke.

The trouble is, with 50 octane fuel if The Piston squeezes too much the heat generated by compression makes the stuff Go Bang prematurely before The Spark Plug gets a look in, giving a Power Stroke with as much push as a fairy’s fart. This is why early engines couldn’t use compression ratios above 4 : 1, and 10BHP per litre was seen as hot stuff.

Engines improved but petrol didn’t and even some time after WW 1 a touring 1000cc engine only turned out about 25BHP, and a hot-shot Sport version with the latest overhead valves would need a good tuner to get 50BHP.

So finally some effort was made to stop primitive petrol going bang too soon, and a variable compression engine was invented for research. (The ‘CFR’ engine, as used for finding Research and Motor Octane Numbers, RON and MON, to this very day.) Early on researchers found that the bung in the CFR head could be really screwed down if a heavy liquid called ‘TEL’ (tetra ethyl lead) was added. This was really effective and cheap, and allowed the ‘straight’ petrol to be upped to 90 or even 100 octane, and a whole load of exciting high-power engines were designed around these fuels.

This leaded fuel survived into the late 1990s, but much earlier an amazing discovery had been made. The shape of the petrol molecules was very important. ‘Octane’ if the ‘straight eight’ version with 8 carbons in a row had an ‘octane number’ of 25. It was only the mutant octane with 5 carbons down the middle and the others sticking out from the sides that gave the best results at high compression. (This special octane is still used as a standard for 100 octane. Proper name is 2,2,4-trimethyl pentane.)

Today, ‘petrol’ is really a synthetic fluid built up from oil industry feedstocks. Very little of it is unmodified distillate from crude oil. It is tailor made to include the best compression-resisting molecules so that no poisonous and polluting lead compounds are needed to reach 95 or even 98 octane. Nothing much is added, apart from a touch of detergent to keep the engine top end clean. Quite a lot of petrol now has 5% ‘renewable’ alcohol as a planet-saving gesture, but this also improves the octane number (by about 1 ) so there’s nothing wrong with that.

Anyway, if you have a motoring holiday instead of flying ComaJet, you are keeping that carbon footprint down….and paying too much tax as well…..but that’s another story.

Fascinating stuff.

Cheers Guy (opieoils)

Oil advice for modifiers and track addicts

If you are modding your car and adding BHP or using it off road then consider your oil choice carefully as the stock manufacturers recommended oil will not give you the protection that your engine requires.

A standard oil will not be thermally stable enough to cope with higher temperatures without "shearing" meaning that the oil will not give the same protection after a couple of thousand miles as it it when it was new.

Let’s start with the fundamentals. An engine is a device for converting fuel into motive power. Car enthusiasts get so deep into the details they lose sight of this!

To get more power, an engine must be modified such that it converts more fuel per minute into power than it did in standard form. To produce 6.6 million foot-pounds per minute of power (ie 200 BHP) a modern engine will burn about 0.5 litres of fuel per minute.(Equivalent to 18mpg at 120mph). So, to increase this output to 300BHP or 9.9 million foot-pounds per minute it must be modified to burn (in theory) 0.75 litres.

However, fuel efficiency often goes out of the window when power is the only consideration, so the true fuel burn will be rather more than 0.75 litres/min.

That’s the fundamental point, here’s the fundamental problem:

Less than 30% of the fuel (assuming it’s petrol) is converted to all those foot-pounds. The rest is thrown away as waste heat. True, most of it goes down the exhaust, but over 10% has to be eliminated from the engine internals, and the first line of defence is the oil.

More power means a bigger heat elimination problem. Every component runs hotter; For instance, piston crowns and rings will be running at 280-300C instead of a more normal 240-260C, so it is essential that the oil films on cylinder walls provide an efficient heat path to the block casting, and finally to the coolant.

Any breakdown or carbonisation of the oil will restrict the heat transfer area, leading to serious overheating.

A modern synthetic lubricant based on true temperature-resistant synthetics is essential for long-term reliability. At 250C+, a mineral or hydrocracked mineral oil, particularly a 5W/X or 10W/X grade, is surprisingly volatile, and an oil film around this temperature will be severely depleted by evaporation loss.

Back in the 1970s the solution was to use a thick oil, typically 20W/50; in the late 1980s even 10W/60 grades were used. But in modern very high RPM engines with efficient high-delivery oil pumps thick oils waste power, and impede heat transfer in some situations.

A light viscosity good synthetic formulated for severe competition use is the logical and intelligent choice for the 21st century.

You must seriously consider a "true" synthetic for "shear stability" and the right level of protection.

Petroleum oils tend to have low resistance to “shearing” because petroleum oils are made with light weight basestocks to begin with, they tend to burn off easily in high temperature conditions which causes deposit formation and oil consumption. As a result of excessive oil burning and susceptibility to shearing (as well as other factors) petroleum oils must be changed more frequently than synthetics.

True synthetic oils (PAO’s and Esters) contain basically no waxy contamination to cause crystallization and oil thickening at cold temperatures. In addition, synthetic basestocks do not thin out very much as temperatures increase. So, pour point depressants are unnecessary and higher viscosity basestock fluids can be used which will still meet the "W" requirements for pumpability.

Hence, little or no VI improver additive would need to be used to meet the sae 30, 40 or 50 classification while still meeting 0W or 5W requirements.

The end result is that very little shearing occurs within true synthetic oils because they are not "propped up" with viscosity index improvers. There simply is no place to shear back to. In fact, this is easy to prove by just comparing synthetic and petroleum oils of the same grade.

Of course, the obvious result is that your oil remains "in grade" for a much longer period of time for better engine protection and longer oil life.

If you would like advice then please feel free to ask.

Cheers Guy (opieoils)