Diesel Fuel, Air Vapors And Your Engine: 2nd in a series of articles
On most EUI injectors, the tappet and tappet spring lift the plunger and pull supply back into the plunger cavity.
Low fuel supply pressure from plugged fuel filters can cause cavitation damage to injector poppet valve during injector fill.
Fluid trapped between the tip and check at the end of injection acts as a shock absorber, minimizing check impact.
An air bubble in the tip provides no fluid damping, allowing the check to impact the tip with up to 50% greater force.
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 found out how the entrained air/vapors get in the fuel and how they affect performance and injector wear.
In our second interview we will learn how what effect entrained air/vapors have on a diesel engine, mechanically and performance wise.
Q. Movin' Out: Brad, how does entrained air/vapor affect a diesel engine mechanically?
A. Brad: Probably the most damaging area affected by entrained air/vapors is the engine's fuel injectors. One of the functions of diesel fuel is to lubricate the injectors as they are working. As the entrained air/vapor passes through the injector it is not providing complete lubricity.
This lack of lubrication for the injector's barrel ad plunger becomes even more critical with the tight tolerances and high fuel pressures used in today's injectors. The entrained air/vapor creates a metal on metal situation. Over time the plunger can start to stick and as it wears, factory tolerances are lost. This causes fuel blow-by in the injector. According to Caterpillar's handbook, entrained air/vapor can create up to 50% greater forces by the plunger on the injector tip. As the fuel comes out the injector tip under high pressure the entrained air/vapor can also act much like an acetylene torch, eroding the injector tip. These two things in combination can lead to the injector tip breaking off.
Entrained air/vapor also causes a degree of implosion in the injector tip, loosening microscopic metal particles from the tip's interior. The gear pump will also experience a degree of gaulding and scoring due to entrained air/vapors. The engine will have a gradual loss of fuel pressure and eventual gear pump failure.
Q. Movin' Out: What are some performance issues caused by entrained air/vapors?
A. Brad: Fuel injection is the process of injecting a predetermined amount of fuel at a predetermined time for a controlled combustion event. Since solid fuel is not compressible but air/vapor is, any air in the fuel is throwing off and retarding the engine timing.
The majority of technical manuals for diesel engines point out that the following problems can be caused by fuel and air restrictions: low horsepower, low fuel mileage, inconsistent performance, hard starts, rough idle, excessive smoking and etc. Simply put, entrained air/vapors do not allow the engine to perform in the working environment as well as they do in the factory. The truck may seem "sluggish" while pulling hills, especially after the fuel in partially filled tanks has time to slosh around and heat up thus entraining air/vapors. You may experience more engine and cab noise than normal and the engine may be a little rough when idling.
The entrained air/vapor problem is one that OEMs are not prepared to deal with. Since the amount of air and vapor that is entrained is changing constantly, there is no way to adjust ECMs to compensate for it nor does the problem show up in the R&D lab. Fuel sources at test facilities are usually above ground-mounted tanks that gravity feed fuel to the pump and eventually to the engine. In a truck's real world working environment, every fuel system's challenge is working against gravity to draw the fuel uphill and forward nearly 8-12 feet to the injectors.
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 learn how entrained air/vapor is removed from diesel fuel using the FASS Fuel Air Separator System.
Kevin Rutherford of ATBS, Bruce Mallinson of Pittsburgh Power, as well as thousands of Class 8 truck and diesel pick-up truck owners endorse the FASS System.
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 –
- FASS Diesel Nationals, Indianapolis, IN
- Dodge Pick-up Show, Pahrump, NV
- TS Outlaws, Bowling Green, KY
- Ballie Diesel Racing, Springfield, MO