Cetane Number – What it is and Why it’s so Important

Cetane Number – What it is and Why it’s so Important

Cooperative Fuel Research Engine (CFR)

Cetane is a measurement of a diesel fuel ignition and or combustion quality. This Cetane Number or CN is one of several components that determine the quality of diesel and biodiesel fuels. This number is used for light and middle distillate fuels. For heavy (residual) fuels Calculated Ignition Index (CII) and Calculated Carbon Aromaticity Index (CCAI) are used.

In some ways this measurement is similar to the Octane Ratings given to gasoline. In its simplest terms Cetane Number measures the delay between the start of fuel injection into the combustion chamber and the beginning of compression ignition (Auto-ignition).

In medium and high speed diesel engines (this all automotive and truck engines) fuel needs to have a CN between 38 and 55 to operate. In general the higher the CN number, the better for the engine and for emissions. However raising CN above 55 currently offers little if any benefit.

In the US the group setting the standards for CN is the American Society for Testing of Materials (ASTM) and currently the minimum is 40. While diesel engines will start and run with 40 CN fuel, they do not run as efficiently as they will at a higher number.

In Europe the European Union (EU) has systematically over several years raised the minimum from 38 to the current 51. This has allowed engine manufacturers to produce more efficient engines with lower emissions and better economy. Most fuel in the EU has a CN of 55 or even better.

Cetane Number is measured using a very expensive and arcane Cooperative Fuel Research (CFR) engine and a process that very complex.

You can also measure CN using an Ignition Quality Tester (IQT) which is somewhat less complex, but still quite costly.

There is a third measurement called Cetane Index (CI) that measures density and distillation range of the fuel and through a calculation provides a measurement. This method will calculate a reasonably accurate number for the refined diesel.

The problem is that today most diesel fuel uses additives to reach the desired Cetane Number and additives do not affect the density, thus the CI of a fuel containing additives is not accurate.

Some of you may have seen a device that looks like a battery fluid tester (a hydrometer). These devices are not capable of determining CN or CI with any accuracy.

You can raise CN by altering the refining process or through the use of Alkyl nitrates or di-tert-butyl peroxide additives. NOTE: Remember that additives do not raise CI.

Also, biodiesel, depending on the base oil from which it is derived has a natural Cetane Rating of 46 to as high as 60.

With the advent of Pilot or Multiple Pulse fuel injection, Cetane Number becomes more important than ever. The delay in auto-ignition (CN) affects the combustion timing, which has a significant effect on power output, fuel economy, and emissions.

Raising Cetane Number together with Improving Fuel Atomization is the fastest way to improve fuel economy and reduce emissions through the use of correctly formulated additives.

Please post your comments, ideas, and suggestions

More information at: http://www.lcbamarketing.com/ - Click on Fuel School Articles.

Diesel Doctor

Copyright 2009© - William Richards

Root Cause Failure Analysis

Root Cause Failure Analysis

Diesel fuel has been identified by at least one OEM as a Root Cause of Engine Fuel System (pump and injector), EGR, EGR Cooler, Sensor, and Turbocharger failures.

Ford Motor Company recently issued a new TSB (Technical Service Bulletin) regarding vehicles using the 6.0 Liter PowerStroke engine.

TSB 08-2-7 stating that “Some vehicles with a 6.0L diesel engine may exhibit white smoke, black smoke, lack of power, exhaust odor, surges, or no start as a result of excessive coking deposits (un-combusted or incompletely combusted hydrocarbons). The root cause of the coking must be corrected or the coking may reoccur”.

They further state: “Coking deposits are generally un-combusted or incompletely combusted hydrocarbons and can form on system components such as the EGR Valve, EGR Cooler, EBP Sensor, EBP Tube, Intake Manifold, Turbo Charger, Catalytic Converter, and EGR Throttle Plate”.

“Un-combusted deposits can be linked to delayed combustion events. Delayed combustion events can be a function of hard to ignite elements (poor quality fuel, excessive fuel, engine oil, or excessive exhaust gas recirculation) in the combustion chamber or a delayed injection event (calibration, wire chafe, injector mechanical issue (Sticktion)).

“Un-combusted fuel is usually evident as a fuel scented white exhaust smoke. Un-combusted fuel may create coking which impairs system functionality eventually leading to black exhaust smoke/poorly combusted fuel”.

In situations where injectors have built up carbon deposits to the point of not being able to properly atomize the fuel, or EGR Valves that have coked or “carboned” up to the point of no longer being able to regulate the Exhaust gas Recirculation, or EGR Coolers that have plugged, to Turbochargers coked to the point of no longer being able to vary their geometry; common practice has been to replace very expensive parts.

Later some companies developed systems to “flush” the EGR’s and Coolers. Flushing will temporarily improve the operation of the engine, however this type of repair lasts only a short time and the initial problems usually reoccurs.

Oftentimes the same parts are replaced many times and then you have the problem where the one part that is not functioning correctly causes other related parts to fail.
In these instances it is vitally important to determine the root cause of these failures. There is a suggested method to do this:

1. 
   Define the problem.
2. 
   Gather data/evidence.
3. 
   Ask why and identify the causal relationships associated with the defined problem.
4. 
   Identify which causes if removed or changed will prevent recurrence.
5. 
   Identify effective solutions that prevent recurrence, are within your control, meet your goals and objectives and do not cause other problems.
6. Implement the recommendations.
7. 
   Observe the recommended solutions to ensure effectiveness.

Today the Root Cause of 80% to 85% of the diesel engine fuel system related problems is poor fuel quality and fuel characteristics.

In the case of the problems described above on the Ford 6.0L and most of the fuel system and related problems found with other diesel engines, the Root Cause of the Failure is poor fuel quality.

You can replace parts and flush till the cows come home and you will continue to have the same problems over and over and over again.

Note: Albert Einstein once described insanity as: “Doing the same thing over and over again and expecting different results”.

Ford has recommended the use of a Cetane Booster and Performance Improver to improve fuel quality and reduce coking and un-combusted fuel problems.

This is not a Ford only or PowerStroke only problem. Every engine manufacturer has to deal with these problems in one form or another.

Use of Diesel Fuel Additives - Year Round

Use of Diesel Fuel Additives
or
Additives's it’s not just for winter anymore

Once upon a time diesel engines were relatively simple pieces of big heavy, hard to break iron. You could put almost anything from kerosene to heating oil in them and they would run, maybe not well, but they would run.

Diesel fuel was considered a residual fuel, something left over from making the good stuff (gasoline). It was not supposed to be a good fuel; it was supposed to be a cheap fuel.

Even if this fairy tale was ever true (it actually was not), those days are long, long gone. Diesel engines today are as sophisticated as those of the worlds fastest Formula One race cars. These engines can have fuel system pressures of up to 35,000 psi and injector machining tolerances of 2 microns or less. Fuel filters that used filter down to 30 or 10 microns, now regularly filter down to 7, 5, and even 2 microns.

The new Ultra Low Sulfur Diesel (ULSD) that is now on the market is derived using various Catalytic Cracking refining processes that affect the quality of the fuel on many levels. The “new” ULSD has less oxidative stability, holds more suspended water, forms gums, varnishes, and carbon deposits more quickly, has less lubricity, gels at higher temperatures, is less thermally stable, is more corrosive, and in general is much more problematic.

In short the quality of the fuel has not kept up with the sophistication of the engines.

As a result you can no longer expect untreated fuel to meet the needs of your engines.

It is no longer good enough to treat your fuel just when it is cold outside. The needs for additional lubricity, higher Cetane, water dispersion, higher levels of oxidative and thermal stability, fuel injector cleaning, corrosion inhibition, fuel atomization require continuous year-round treating to protect your equipment and to maximize performance.