How Common Rail Fuel Systems Work

High pressure common rail fuel (HPCR) systems come with pretty much ever diesel engine in this day and age, from heavy equipment to over the road trucks, light duty trucks, large generators and a plethora of other systems, they all have them. The HPCR systems prove very beneficial but do not come without their cons. These systems have confused many operators, leading to instances of destroyed fuel systems due to operators putting contaminated fuel into their machines.

To make sure that the engine keeps running as it should be, it is imperative to know the fuel systems inside out, including their sensitivity and consequences of contaminated fuel. Therefore, it
would be helpful to know the warning signs.

Pros and Cons

The HPCR system is comprised of a high pressure fuel rail that is common to all the injectors. The fuel is delivered to the high pressure fuel rail via a high pressure supple pump. The pressure in the rail can reach between 30,000 – 40,000 psi dependent on both the rpm and engine load. Additionally, the injectors are electronically controlled, and each own their own firing mechanism or solenoid.

Due to how the HPCR systems are designed, they achieve a better atomization of the fuel when injecting to deliver a cleaner, more powerful and complete combustion. The engines that already have a HPCR system installed can achieve a cleaner exhaust, more horsepower, and more fuel efficiency per displacement in comparison to previous models.

Some people claim that a downfall of these HPCR systems is their complexity with regard to their electrical components. This is because the HPCR comprises of a number of sensors, wiring harnesses and electrical parts that need to be added to make sure the engine runs as it was intended. Another supposed downfall is their sensitivity to contaminated fuel.

Prior to the Tier 4 emission requirements, non road diesel engines employed a mechanical injection system. These systems however were not known to be as vulnerable to contaminated fuels. Due to this, the HPCR fuel systems were tarred with the same brush of being just as resistant to contaminated fuel. However, unfortunately this is false. These newer diesel engines can easily be damaged by dirty or incorrect fuels, water in the fuel and air in the system.

To reiterate, the HPCR systems are easily damaged if due care is not carried out and considered. The reason behind this is because the greater the injection pressure, the stricter the tolerances must be between the mating parts in fuel-handling components like pumps, injectors and valves. Tighter tolerances make these precision surfaces extremely susceptible to being harmed by almost anything that’s not the correct fuel. although, a certain amount of contamination or water will not cause the system any damage in the older mechanical injectors, but that same fuel had the potential to cause carnage in a common rail fuel system.

Effects of contaminated fuel

The primary problem that causes damage is when water manages to work its way into the fuel. This can be caused by instances like improperly maintained transfer tanks. These tanks have a number of issues:

• Sometimes, they hardly ever get drained.
• The water gathers in the tank from condensation.
• The location of the tanks and the environment service trucks can find themselves in, mean they can collect heavy debris. Therefore, it’s crucial to clean the fuel cap and near areas before filling the transfer tank.
• If the tank is not maintained properly, the water content will continue to increase and could lead to cause rust inside the tank and lines.
  To aid these problems, equipment companies and manufacturers have included fuel and water separators in their machines. Although, this is not sufficient to completely remedy the problem on its own. It needs to be examined and drained daily, failing to do so will mean the water level will rise to the top of the separator to then being forced through and back into the fuel system effecting the vital components of the system.

Water reaching the fuel can have numerous impacts of different areas of the machine:

• In some instances, free water can be driven into the injector. Excessive heat in the injector will cause this water to turn into steam and therefore expand, which will then cause a failure in the injector tip.
• Excessive heat in the injector will cause the water to turn into steam and expand, triggering a failure in the injector tip.
• Any damage to the needle valve can stop it from correctly sealing when shut. This permits non-atomized fuel to seep onto the piston surface, causing a melted piston.
• Other contaminates, such as dust particles and low-quality diesel fuel with low lubricity properties, will also damage the fuel system.
• Commonly, this will decrease the lubricity of the fuel. This will cause harm to the needle valve situated inside the injector, which will then become sticky and result in high return flow or high fuel delivery.
• Fuel directly injected into the cylinder wall will mean cylinder wash, which is when the fuel washes the lubricant oil away. The consequence is poor lubrication between the piston and cylinder wall, that will cause wear. This unavoidably leads to low compression, oil dilution and engine failure.
• The needle valve can also be damaged to the point it no longer seals as it should, therefore, allowing the injector tip to seep.
• Metal from the needle valve damage or from other component damage can clog the nozzles, causing a distortion of the spray pattern. This in turn will cause fuel being sprayed straight onto the piston surface or cylinder wall.

Due to all the reasons above, it is imperative to keep a clean and healthy fuel system by frequently changing the fuel filters. In the case of Takeuchi, every machine has one to two fuel filters and a water separator. However, while very effective at removing damaging contaminants and water, fuel filters will fail to work effectively if they are not serviced regularly. Making sure that clean fuel is being used is the single most important step toward keeping your system healthy. Other steps you take to achieve this is to use a credible source that you know delivers clean and filtered fuel, upon filling, it is vital you fill the neck screen in place to avoid foreign objects from entering the tank. In the instance of debris entering your tank means it could restrict the fuel flow from the tank, or depending on the type of debris, break down into fragments and cause more fuel system issues.

Warning Signs

In most instances, the first symptom of engine failure due to fuel contamination is multiple failed injectors. Indeed, these are the same components, but they operate separately and only share one commonality – the fuel source. If an operator happens to notice hindered engine performance, excessive smoke, unnecessary regeneration requests or other abnormalities it is advisable to stop the engine before any serious damage can be done. The most undesirable outcome for any machine owner would be downtime due to failure. Some things in life are easily fixed, but unfortunately an engine is not one of these things. In fact, it will also cost a lot more than minor work interruption. So, the moral of this story would be to use clean and filtered fuel of the upmost quality, saving thousands in repair costs and stress.