Find Your Vehicle
Rating Diesel; Understanding Cetane Numbers
Hydrocarbons, a compound comprised of carbon and hydrogen, typically make up the bulk of various petroleums. Cetane is one such hydrocarbon that appears in a colorless fluid form. When it comes under extreme compression, the pressure causes it to ignite quite quickly. Cetane is assigned the base rating of a hundred. Accordingly, it is then used as a measurement to indicate how well other fuels, like diesels or even biodiesels, perform.
What Does Cetane Number Indicate?
Standard gasoline uses a rating system of octane numbers to measure its efficiency. In a similar manner, diesel uses cetane numbers as a measurement of how well it combusts. However, there is a significant difference in what exactly these two ratings measure. For gasoline, the octane number measures how well the substance will resist spontaneously combusting at average temperatures without a helper ignition source. This is known as auto-ignition. Comparatively, the cetane number (or CN for short) tests how long the diesel delays its ignition time after the fuel enters the combustion chamber.
Since diesel works with compression instead of a flame or spark, it is most effective when it ignites as quickly as possible. If it has a high cetane number, this means that the delay period is relatively short. In this case, the short delay period allows the diesel to burn more completely. In turn, it helps the vehicle’s engine to run more smoothly and powerfully while producing less emissions. Diesel that takes a longer time to ignite does not work as efficiently. Keep in mind that the cetane number is mostly used for lighter diesel fuels. The efficiency of heaver diesel is measured using a couple of other ratings called the CII and CCAI.
How is the Cetane Number Test Calculated?
There are a number of tests and special procedures that are used to measure cetane ratings. This typically involves engines used specifically for testing purposes, as well as running an analysis of the diesel under varying conditions. However, these methods are not only costly, but they also take a great deal of time and effort. As an alternative, there is another process called the calculated method for finding the cetane number of a fuel. Within the calculated method are many different tests that can be run. One such test that is most commonly used is known as the ASTM D976. Another popular one is called the ASTM 4737. Both of these processes derive cetane numbers by measuring not only the fuel density, but also its boiling and evaporation levels.
What Effect Does the Cetane Number Have on Engine Performance?
With standard cars, it generally does not benefit the engine if the driver fills it with a gasoline that features an octane rating more than the amount recommended by the manufacturer. Similarly, vehicles that run on diesel do not perform any better by using fuel with a cetane number higher than the recommended amount for that specific engine. Despite this, there is sometimes a misconception that any higher cetane number will result in better engine performance and power.
There are many different factors that are involved in determining the best cetane number for a certain type of engine. This normally includes the physical size of the engine, the way it is designed, how fast it operates, as well as its load variations. A less factor, but one that is counted all the same, is external weather or climate conditions. On the other hand, if an engine is operated with a fuel that features a cetane number lower than the recommended amount, there can be several drawbacks. The vehicle will not operate as smoothly, and the poor operation can result in vibrations as well as extra noises. Additionally, it could create a larger amount of emissions and wear on the engine. In some cases, the driver may even have difficulty starting the engine.
Types of Diesel Fuels and Corresponding Cetane Numbers
Most diesels for standard vehicles and general highway usage normally require a cetane rating that falls between 45 to around 55. The table below outlines the different grades of cetane numbers that correspond with various diesel fuels that are compression ignited.
|Types of Diesel||Cetane Numbers|
|Biodiesel Blend (B20)||50|
“I must say l'm delighted with the improvement from your chip, its on the standard settings and the difference in the car is amazing!!! I have a smile on my face every time I get in the car, and there is about 5-7mpg improvement. With the mileage l do, l can see myself getting my money back in no time at all. So if your a doubter like me, don't be because its one of the best things l've ever bought!!!”
Ian from Manchester
Audi A6 MK4 3.0 BiTDI 313
“Many thanks for your fantastic service! Unit ordered Sunday, delivered Tuesday am!! Unit now fitted and, as promised, the car is transformed. Winding country lanes tackled quite happily in fifth gear. Cruising on much smaller throttle openings and immediate response on acceleration. The car behaves as a mini car should behave. I had some initial doubts about spending quite a large amount of money on this item but it is worth every penny and would not hesitate to advise anyone to do similar.”
Alan from Coventry
Suzuki Swift 1.3 DDIS 75
“I was a sceptic at first, then after reading the experiences others had been through I decided to give it a go. I bought a new 1.7 CRDI Sportage, not the 2ltr purely for better fuel figures. Whilst this engine pulls very well in standard form, and was returning 44-45mpg even during the first 500 miles I had to go down the CHIP Express route. Well, there is absolutely no point in forking out the extra 2 grand for the 2 litre model when you can get the 1.7 and spend much less to get 2 litre power figures. Excuse the cliché’s, but this car is transformed and by a big margin too. From what I can remember about my 2 litre test drive, my 1.7 now pulls better than the 2 litre version. The low-down grunt is remarkable and pulls like the proverbial train. Fitting took minutes and was effortless, the box was kept on factory settings, I feel there is no need to mess with it. Needless to say I am now a very happy boy and would without question take this route again. I would recommend this to any diesel Sportage owner. Many, many thanks for a remarkable product and a customer service that is rare in this country!”
Ron from Thetford
Kia Sportage MK3 1.7 CRDI 116
“Your customer service, speed at which you deal with questions and chip (most importantly) are second to none. This is the 3rd variation of the chip that I have run, not only do I see the fuel savings made each and every time I fill up but I also feel the changes in the increased performance too. Far too often people only feel the need to leave negative feedback on a product, it's very rare that people take the time to leave positive comments however on this occasion I feel compelled to do so. A brilliant product and one that I highly recommend should you want to make the most of your cars potential performance and make a fuel saving to add into the bargain. What's not to like?! It's been a pleasure dealing with the team at Chip Express, I just wish everyone I dealt with in life was this professional! Thank you.”
Lee from Halifax
BMW 1 Series F20 120d 190
“A friend recommended one of your "gadgets" a year ago and being not-very-techno (but Scottish and keen to save money!) I bought one. The gizmo has TRANSFORMED the performance of my Land Rover Freelander 2 TD4 AND improved the fuel economy by a genuine 15%; so much so that I have bought another one for our Freelander 2 SD4 which is now a REAL Q-car! (And of course saves fuel...) I have never written a review before (though strangely I do read them and take notice of them, whilst half-believing that they are written by the owner's chums!) so to have made me pick up pen & paper so to speak - I MUST be delighted! Thanks for making technology so simple and so successful!”
Andrew from Lochwinnoch
Land Rover Freelander (2) SD4 190
“As do many, I took the 'if it sounds too good to be true, it probably is' approach to performance chips. But CHIP Express were recommended by an impeccable source who had had experience with their product on my model of car - a Citroën C6 with the 2.7 HDi twin turbo diesel. Following a first rate response to a query, the product has delivered in spades. Ten days and more than 1000 miles of mixed town, country, low and high speed driving later I am certainly getting more than 10% more from a gallon, and probably 15%, and the performance is markedly better. Low speed response is immediate and has eradicated what I took to be baked-in lag in a big automatic turbo diesel, and mid-range acceleration is silky smooth, including up inclines. A very good car has been turned into the excellent car I had hoped for all along.”
Simon from Ketteringham
Citroen C6 2.7 HDi 204