Diesel Fuel, Air Vapors And Your Engine: 1st in a series of articles
By Steve Pollock
MARTHASVILLE, MO....Today's diesel fuel presents many challenges to a truck owner besides the "High Price." While cetane levels, lubricity, water, dirt particles and waxing have all been discussed in detail, entrained air/vapors in the fuel have not. Although comprehensive data is available through such companies as Cummins, Detroit, Caterpillar, Racor, MSOE (Milwaukee School of Engineering the foremost school of hydraulic engineering) and other fortune 500 companies, this data is hard to discover in public articles. Brad Ekstam, President of Fass Fuel Systems and an expert about diesel fuel and entrained air/vapors, has volunteered to enlighten us in a series of interviews. In our first interview with Brad we will find out how the entrained air/vapors get in the fuel. Other interviews will discuss how they affect the fuel injection components, how the entrained air/vapors are removed and the benefits associated with doing so.
Movin' Out: How do entrained air/vapors become mixed with diesel fuel?
Brad: There are a couple of sources that entrained air/vapor is introduced into diesel fuel. The first is agitation: As you travel down the road the fuel is agitated, the longer you travel the more air. This in most cases is where the majority of air is developed. Also, the return fuel pouring in the top of the fuel tank is introducing more agitation, simply, agitation occurs as you are driving. In a little over an hour, the amount of entrained air present in the fuel is equal to the amount of vapor being produced when fuel is subjected to 11 1/2" of vacuum. In turn, creating even more of an air issue, this brings us to the 2nd source of entrained air/vapor – "VAPOR." With some exception most brand new filters "Clean," are rated at about 5" of restriction. As a fuel filter restricts, the amount of vacuum increases causing what we know as fuel starvation. Fuel starvation is "VAPOR" being produced from the fuel equating to less fuel and more air replacing where fuel should have been. Food for thought – remove the dirtying fuel from your truck and replace it with a new fuel filter, engine performs much better. Yes, this is due to less restriction; now imagine even cleaning the new filter to where there is "NO" restriction, i.e. like in the manufactures test cell!! Research from both Cat and Cummins both confirm that diesel fuel itself contain as much as 3-10% air.
One easy place to identify that air/vapor is in the fuel, and many truck owners ask themselves this, why is my suction side fuel filter almost never full of fuel when it is removed? This tells you that you always have entrained air/vapor entering your engine. We'll be covering this later in this series of articles.
Physics are also at work. Diesel fuel loses viscosity and lubricity as it heats up causing the fuel to expand and become "thinner." The thinner a liquid, the more air/vapor is created but the less air it entrains. With thicker or cooler liquids, less air vapor is created but more is entrained. Vacuum and pressure also affect this equation, pressure to fuel raises the boiling point and vacuum lowers it. Boiling Point - You may be asking yourself?? Restriction on fuel lowers the boiling point, i.e. more vapors. Pressure/less restriction on fuel increases the boiling point, i.e. less vapors. A plugging fuel filter will create more air/vapor, as the vacuum increases to the fuel pump. The fuel pump is not working as efficiently.
Movin' Out: Why are air vapors a problem?
Brad: Air vapors entrained in the fuel can create a degree of fuel starvation for your engine. Have you ever heard your engine "miss or idle rough" while idling? This is air entering your injector and throwing the timing off of when the fuel actually enters the combustion chamber, causing an inefficient burn or "miss." The symptoms you may experience traveling down the road maybe more cab noise, less power, laboring to pull hills as well as it did earlier in your travels. The truck is experiencing a loss of performance, which equates to lost horsepower and a loss of fuel mileage. Another by-product is increased emissions – i.e. smoking. There are mechanical ramifications as well. Research by Caterpillar has shown that air can cause up to 50% greater force of the plunger on the injector tip, occasionally causing the injector tip to blow off.
The air/vapor in the fuel will also cause excess cavitation to the injector nozzle that can lead to premature injector failure. A degree of “implosion” is also created within the injector housing, adding to wear. The additional loss of lubricity caused by the air/vapor will also create gaulding and scoring of the injectors.
The air/vapor problem in diesel fuel is for the most part off the OEM radar screen. A controlled environment during the testing process is the culprit. Most OEM test facilities test the engine itself in a lab. Ambient temperatures are stabile, and the fuel is gravity fed from a tank mounted on the roof or well above ground that contains thousands of gallons of fuel. Since the engine is stationary, agitation in the fuel tanks is a non-issue. Variations in fuel pressure and vacuum are also eliminated.
Here are a couple of things to try with your own truck:
- Pay attention the next time you fill your fuel tank. You may be able to notice increased performance with a full tank of cooler fuel. As the fuel level in the tank depletes and the fuel entrains more air, you will experience a reduction in performance.
- While filling up fill up your primary fuel filter with fuel (section side). Pay attention to the engine’s performance and experience how it will perform better for about the next hour. After about 1 – 2 hours after that you’ll notice the performance falling off. If possible, stop and pull the filter off and see how much “empty” headspace is in it. Refill with fuel and see your performance improve. This is a small taste of what the FASS does.
Entrained air/vapors are an inherent problem for all diesel engines, including Class 8 trucks, pick-up trucks, marine engines & etc. In next month’s article we will summary this issue and the variables & discuss how entrained air is removed from diesel fuel using the FASS System. The FASS System is endorsed by Kevin Rutherford of ATBS, Bruce Mallinson of Pittsburgh Power, as well as thousands of Class 8 truck and diesel pick-up truck owners.
The folks at FASS Fuel Systems welcome your questions and comments. You can call their technical department at 636-433-5410 or email them at firstname.lastname@example.org. They would also like to invite you to attend the FASS Diesel Nationals, which will be held on June 5th at The O'Reilly Raceway Park in Indianapolis, Indiana. Log onto www.nhrda.com for more information.
You can also visit FASS Fuel Systems at the following trucking and pick-up truck events:
Semi Trucking Shows –
- Walcott Truckers Jamboree, Walcott, IA
- All Truck Nationals, Carlisle, PA
- Great American Truck Show, Dallas, TX
- Canadian Truck Rodeo, Quebec, Ontario
Diesel Pick-Up Shows –
- Dodge Pick-up Show, Pahrump, NV
- TS Outlaws, Bowling Green, KY
- Ballie Diesel Racing, Springfield, MO
- FASS Diesel Nationals, Indianapolis, IN