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ChrisW United Kingdom

Wed Sep 15 2021, 01:21pm

Joined: Jun 18 2013

Member No: #1335

Location: Surrey

Back in 2012, speedfix recommended the use of premium diesel and adding 2-stroke oil (2-T) when filling up (I wish I'd seen his post back then). If it’s good enough for speedfix, it’s good enough for me! So, when I saw his post recently, I tried it at my next fill. The effect was amazing – the engine was much quieter with no diesel knock. Was this merely a placebo effect, though? I had tried premium diesel before and seen no benefit, so the benefit must be from the 2-T.

There’s load of stuff about this on the internet. There are two camps. Those who say they have never tried it and never will – they have nothing to add to the debate. Those who have tried it – some say it made no difference but most reported benefits, in particular less noise. None who tried it reported any damage to the engine. The standard ratio is 1:200, 2-T to diesel.

So, what could explain the effect of 2-T? I’m a chemist but combustion chemistry is very complex, so my take on it will be fairly broad brush. It’s all about carbon chain length (eg. C10 is a chain of 10 carbon atoms).

Diesel is typically 36% C10-12, 49% C12 -16, 15% C16-35.
2-T is typically 18% C10-12, 4% C12 -16, 65% C16-C35, 13% C35-40
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Adding 2-T increases the chain length of the mixture. This affects the ignition delay and flame speed. As the graph in Figure 1 of this report shows, increasing the chain length reduces the ignition delay.
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The reason why diesels knock when cold is because the prolonged ignition delay from a cold engine allows more fuel to enter the cylinder before it ignites, resulting in a bigger bang. Reducing the delay results in a quieter engine.

Increasing the chain length of hydrocarbons means they burn slower. Add 2-T, therefore, means that ignition starts quicker but the burn time increases. This gives smoother combustion. I am now confident that the benefit for is real and not placebo.

My concern was ash. When diesel burns it leaves only 0.01% ash. Even low-ash 2-T (JASO FD) has 0.18% ash. Adding this 2-T at a ratio of 1:200 results in a 9% increase in ash from the mixture. Of particular concern is zinc, which is a common oil additive and has been shown to foul injectors. Fortunately there is a solution. As you can see from the graphs in this website, Archoil AR6900D prevents and removes zinc deposits on injectors.
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I now add 1:200 2-T (CASTROL Power 1 2T, JASO FD) and 1:1000 Archoil to bog-standard diesel every time I fill. My C6 runs better than it has ever done. I hope this was of interest. I apologise for the length of my post, but I though a bit of science might inform the debate on the subject.


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