SPECIAL OFFER: Buy today and get FREE shipping worldwide on any order! No minimum purchase required.

Rating Diesel: Understanding Cetane Numbers


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
Regular Diesel 48
Premium Diesel 55
Biodiesel (B100) 55
Biodiesel Blend (B20) 50
Synthetic Diesel 55

Any questions?

We're here to help! So contact us, or read our FAQs.

Order Today

It takes minutes to order and minutes to fit, so why wait? Buy now with complete confidence!

Find Your Vechicle »

What others are saying...

“Be assured, this is NO gimmick. Arrived yesterday (less then 24 hours after the order was placed) and fitted today. The fitting was easy especially with the photos and instructions sent with the chip. The first thing I noticed was the responsiveness of the engine from a standing start, no more lag. I then went on a 30 minute drive both motorway and sideroads and my average fuel consumption went UP from 33.3mpg to 38.7mpg. My motorway speed varied from 60 to 85mph and the sideroads from zero to 40mph. I am so pleased with the whole result. This is worth every single penny paid. Thank you!”

★★★★★

Edwin from Bridgend

Ford Kuga MK2 2.0 TDCi 163

“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

“May I congratulate you on this diesel tuning product as it has made a noticeable difference to my Land Rover Discovery. I have tried other diesel tuning boxes for my previous vehicles (Kia Sorento, Peugeot 206 and Vauxhall Vectra)... and they all produced slight engine stuttering under certain load conditions. The CHIP Express system does not show any evidence of this and is equal to the likes of an ECU remap (which I have also had done before) for smoothness and noticeable power gains. This would be the only diesel tuning product I would recommend.”

★★★★★

James from Callington

Land Rover Discovery (3) 2.7 TDV6 190

“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

“A good product and a good service deserves recognition: I fitted a CHIP Express unit to my Insignia. What an amazing bit of kit! My fuel economy and performance went way up and with the mileage I do was a Godsend! On a run to Aberdeen from Hull I returned an average of 62 MPG and I drive quite energetically! I've just taken up the trade in offer and saved a few quid on a new system. The Vauxhall has now gone with 125,000 trouble free miles and I have changed car to a Volvo S60 D3. I'm looking forward to fitting the Chip Express unit and reaping the rewards, thanks guys!”

★★★★★

Frazer from Skirlaugh

Vauxhall Insignia MK1 2.0 CDTI ecoFLEX 130

“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