Understanding Common Rail Diesel Fuel Pressure Performance

Common rail direct fuel injection systems are built around a high-pressure fuel rail feeding solenoid valves. These systems can generate pressure in excess of 2,000 bar (29,000 psi), which offers several benefits over traditional diesel systems. The high pressure improves the atomisation of the fuel, resulting in better ignition and combustion within the engine. This leads to improved performance and lower fuel consumption. The electronic control of the injectors also provides greater flexibility, allowing more precise and frequent injections, with up to seven injections per cylinder per stroke.

Injector issues

The high pressure and temperature can also cause fuel degradation, which can form deposits within the injectors and interfere with their fine tolerances, leading to sticking, malfunction, and injector wear. Biodiesel blends are particularly susceptible to degradation, which can further increase the risk of injector issues.

Additionally, the use of low-sulphur diesel fuel can contribute to injector problems. Sulphur provides lubrication, so lowering sulphur levels can result in greater wear on injectors. The fine tolerances within injectors and the high pressure in common rail systems mean that even small amounts of water contamination in the fuel can cause issues.

The frequent injection cycles of common rail systems—up to five injections per firing cycle—can also lead to injector issues. Any delay caused by contamination or poor fuel lubricity can result in excess fuel being pumped into the engine, leading to increased fuel consumption and soot emissions.

To prevent and resolve injector issues, regular maintenance is crucial. This includes using fuel additives to clean and enhance fuel lubricity, as well as routine replacement of fuel filters to ensure system cleanliness.

Fuel contamination

There are several causes of fuel contamination in common rail diesel systems:

• Improper maintenance: Failing to drain the fuel tank before replacing a fuel system component or not keeping the engine bay clean can lead to contamination.
• External sources: Siphoning diesel from a truck can introduce contaminants, and unsecured fuel sources can transfer contaminants to other trucks or locations.
• Water: Water in diesel fuel can come from the service station, moisture in the tank, or even crossing a river. Water can cause a lack of lubrication, rust components, and affect fuel stability.
• Particulates: Dirt, dust, and debris can enter the fuel system during maintenance or refuelling, and even dirty hands and tools can transfer contaminants.
• Non-diesel liquids: Filling a diesel vehicle with petrol or other non-diesel liquids can cause damage to fuel system components.

To prevent fuel contamination in common rail diesel systems, it is important to use high-quality, clean diesel fuel and to test the fuel quality regularly. If contamination is suspected, it is crucial to take immediate action to clean the system and prevent further damage.

The effects of fuel contamination in common rail diesel systems can be felt in various ways, and some symptoms may go unnoticed or be ignored. Clogged fuel filters, fuel pump failure, and partial injector failure are common issues that can lead to catastrophic engine failure. Contaminated fuel can also affect fuel atomization, resulting in increased fuel consumption, reduced power, and higher emissions.

In summary, fuel contamination is a significant concern in common rail diesel systems, and it can lead to costly and dangerous failures. By understanding the causes, effects, and prevention methods, operators can take the necessary steps to maintain fuel quality and ensure the reliable operation of their engines.

Water damage

To prevent water damage, it is essential to maintain the fuel system and use high-quality fuel. Regularly checking and replacing the fuel filter is crucial, as a clogged filter can lead to water buildup. Additionally, ensuring the water separator is functional and draining any water it collects are important preventive measures.

When water contamination is suspected, it is vital to inspect the fuel for signs of separation and look for floating or suspended items. Metal debris, which can result from water contamination, may be challenging to spot. Using a coffee filter or a dark-coloured container can help identify metal particles. If water or metal debris is detected, the fuel system should be thoroughly flushed, the fuel tank cleaned, and fresh, clean diesel fuel used.

Water contamination can cause severe damage to fuel injectors, the high-pressure injection pump, fuel pressure sensors, and control components. It can lead to corrosion, creating a film or residue that erodes injector valve seats and degrades fuel injection performance. Water also impedes lubricity, resulting in metal-on-metal contact and increased wear. Therefore, addressing water contamination promptly and maintaining the fuel system is crucial to the longevity and performance of common rail diesel engines.

High-pressure pump

The high-pressure pump is a critical component of the common rail diesel system, responsible for generating the high fuel pressure

Injector control valve

In a common rail diesel system, the injector control valves receive diesel fuel at high pressure (over 2,000 bar or 29,000 psi) from the common rail, also known as the high-pressure accumulator. This rail stores pressurised fuel that is supplied by a high-pressure pump. The injector control valves, when activated by the ECU, release a precise amount of fuel into the cylinders at the desired pressure. This high-pressure injection results in the fuel being atomised into smaller droplets, leading to more efficient combustion.

The flexibility of the common rail system allows for control over both the injection timing and rate. This means that the injection pressure can be maintained independently of engine speed and load conditions. As a result, the system can deliver better fuel spray penetration and mixing, even at low engine speeds. Furthermore, the ability to inject small amounts of diesel just before the main injection event helps reduce engine noise and vibration.

The injector control valves are typically electronically actuated, which means they can be activated by the ECU at the optimal moment. This electronic control also enables precise adjustments to the injection timing and quantity, ensuring that only the required amount of fuel is supplied to the injectors. This differs from earlier conventional diesel systems, which were primarily mechanically controlled.

Overall, the injector control valves in a common rail diesel system contribute to the improved performance, efficiency, and environmental friendliness of modern diesel engines.

Frequently asked questions