Marine Fuel Injector Valves – Ensuring Optimal Performance

Marine fuel injectors are critical components of an engine’s fuel delivery system, responsible for precisely atomizing fuel and delivering it to the combustion chamber. Over time, these injectors can become clogged, worn, or develop leaks, resulting in decreased engine performance, reduced fuel efficiency, and potential engine damage. In this blog article, we will explore the importance of overhauling and maintaining marine fuel injectors to ensure their optimal performance and prolong the life of your marine engines.

Before diving into the overhaul and maintenance process, it’s crucial to be aware of common signs indicating potential fuel injector problems. These signs include: reduced engine power and acceleration, rough idling or stalling, increased fuel consumption, misfires or engine hesitation, smoke emissions from the exhaust, difficulty starting the engine etc. If you want to learn more about “How to check fuel injector valve condition”, please follow THIS LINK.

Marine engines are subject to strict emissions regulations aimed at minimizing their environmental impact. Maintaining the peak performance and efficiency of marine engines is crucial for a smooth sailing experience. Among the various components that play a pivotal role in engine function, fuel injectors stand out as critical elements. These small but mighty devices atomize fuel and deliver it to the engine’s combustion chamber, directly impacting its power, fuel economy, and emissions.

Fuel injectors must deliver fuel in a precise spray pattern and at the right pressure for efficient combustion. Over time, fuel injectors can develop leaks or clogs that disrupt this delicate balance, leading to suboptimal combustion. By conducting regular leak and pressure tests, marine engineers can identify and rectify any issues promptly. Maintaining the integrity of fuel injectors ensures that the engine receives the right amount of fuel, enhancing combustion efficiency, power output, and reducing fuel consumption.

Leaking fuel injectors can result in serious consequences for marine engines. When fuel leaks occur, excess fuel can infiltrate the engine’s oil system, diluting the lubricating properties of the oil and causing accelerated wear and tear on internal components. In extreme cases, uncontrolled fuel leaks can even lead to engine fires, posing a significant risk to the vessel and its crew. By performing regular leak tests, potential issues can be detected early, preventing costly engine damage and ensuring safe operation on the water.

When fuel injectors leak or malfunction, the combustion process is compromised, leading to incomplete fuel burn and increased emissions of pollutants such as hydrocarbons and nitrogen oxides. Regular leak and pressure tests help maintain optimal injector performance, ensuring cleaner combustion, and reducing the vessel’s environmental footprint.

Fuel injectors that are functioning optimally contribute to overall engine performance and reliability. A leak or malfunctioning injector can result in reduced engine power, rough idling, decreased throttle response, and even engine misfires. Through leak and pressure testing, any injector-related issues can be promptly identified and resolved, allowing the engine to operate at its full potential. A well-maintained fuel injection system ensures smooth operation, enhances engine reliability, and minimizes the risk of unexpected breakdowns.

Overhauling fuel injectors involves a thorough cleaning and restoration process to remove deposits, restore proper fuel flow, and optimize performance.

Here’s a step-by-step guide to overhauling marine fuel injectors:

    • Carefully remove the fuel injectors from the engine, following the manufacturer’s instructions.
    • Examine the injectors for any signs of damage, such as cracked or broken components. Check the injector tips for carbon buildup or clogging, which can impede fuel flow.
    • Utilize a specialized injector cleaning kit or professional cleaning service to remove deposits, varnish, and carbon buildup. Follow the specific instructions provided with the cleaning kit or consult manufacturer or a professional technician.
    • Replace worn or damaged injector components, such as O-rings, seals, and nozzles, to ensure a proper seal and prevent leaks. Use high-quality replacement parts recommended by the manufacturer.
    • After cleaning, perform a comprehensive fuel injector test to evaluate their performance. This test may include flow rate measurement, spray pattern examination, and leak detection. Replace any injectors that fail the test or show significant performance deviations.

    • Carefully reinstall the fuel injectors, ensuring proper alignment and connection. Follow torque specifications provided by the manufacturer to avoid overtightening or undertightening.

Regular maintenance and testing of marine fuel injectors are essential to ensure optimal engine performance and prevent potential issues. One crucial test that should be performed is the fuel injector leak test.

In the next paragraph, I will provide you with a step-by-step guide on how to perform a marine fuel injector leak test, enabling you to identify and address any leaks promptly and maintain the reliability and efficiency of your marine engine.

    1. To perform a fuel injector leak test, you will need the following items:
      • Fuel injector tester or kit
      • Appropriate safety equipment (gloves, eye protection)
      • Fuel pressure gauge
      • Fuel system cleaning solution (optional)
      • Manufacturer’s service manual (for specific instructions and specifications)
    1. Before beginning the test, it is crucial to ensure the safety of the testing environment. Follow these steps:

      • Make sure the engine is turned off and has had enough time to cool down.
      • Locate the fuel injectors on your marine engine. They are usually mounted on the cylinder head.

      • Review the manufacturer’s service manual for any specific instructions or precautions related to your engine model.

    2. To prevent fuel flow during the test, you need to disconnect the fuel supply. Follow these steps:

      • Locate the fuel supply line connected to the fuel rail or fuel distributor.
      • Carefully disconnect the fuel line using the appropriate tools, ensuring that any residual pressure is relieved safely.

      • Use a suitable plug or cap to seal the open end of the fuel line to prevent any fuel leakage.

    3. The fuel injector tester allows you to apply pressure and detect potential leaks. Follow these steps:

      • Connect the fuel injector to the fuel injector test bench according to the manufacturer’s instructions.

      • Ensure a secure and proper connection between the tester and the fuel injectors.

      • Make sure all connections are tight and leak-free to maintain accurate testing results.
    4. Now it’s time to apply pressure to the fuel injectors and observe for any leaks. Proceed as follows:
      • Refer to the manufacturer’s instructions to determine the recommended pressure for your specific engine model.
      • Connect a fuel pressure gauge to the fuel system to monitor the pressure during the test.

      • Gradually increase the pressure to the specified level while monitoring the gauge for any sudden drops or fluctuations, indicating potential leaks.


    5. During the pressure test, carefully inspect each fuel injector for signs of leaks. Perform the following:

      • Visually inspect around each fuel injector for any fuel drips, seepage, or signs of wetness.

      • Use a flashlight if necessary to better observe the injector area and connections.

      • Pay attention to the injector O-rings, connectors, and fuel lines for any signs of deterioration or damage.

If you identify any leaks during the test, it is crucial to address them promptly. Replace any faulty O-rings or damaged injector components. Clean the fuel injectors using a suitable fuel system cleaning solution, following the manufacturer’s instructions. Re-test the fuel injectors after repairs or cleaning to ensure the leaks have been resolved.

Performing a fuel injector leak test is a crucial aspect of maintaining the performance and reliability of marine engines. By following this step-by-step guide, you can identify potential leaks early on, address them promptly, and ensure the optimal operation of your marine fuel injectors.

To maintain the optimal performance of marine fuel injectors between overhauls, consider implementing simple routine maintenance practices, like:

    • proper purifier operation and maintenance, to ensure clean and high-quality fuel, minimizing the risk of injector clogging and deposits.
    • periodically use fuel additives designed to clean and lubricate the fuel system. These additives can help remove deposits and improve injector performance.
    • conduct visual inspections of the fuel injectors during routine maintenance checks. Look for signs of leaks, damaged components, or buildup that may require immediate attention.

In conclusion, marine fuel injectors play a vital role in the performance, efficiency, and longevity of marine engines. Overhauling and maintaining these injectors ensure proper fuel delivery, optimal combustion, and reliable engine operation. By following the steps outlined in this blog post and implementing routine maintenance practices, you can maximize the performance and lifespan of your marine fuel injectors. Remember, a well-maintained fuel injector system translates into a smoother, more efficient, and trouble-free vessel operation experience.

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What you need to know about main engine continuous low load operation

I believe that many of you, have heard in the last couple of years about running the main engine at low load or slow steaming due increasing fuel price and lately due more stringent environmental regulations.

The 2-stroke engines are designed and optimized for operation in the load range above 60 % CMCR, but is possible to use them at continuous low loads down to 10% CMCR if we pay special attention as they are some recommendations on what needs to be observed when operating the engine at loads lower than 60 % CMCR.

It is very important to be aware that at lower engine load between approximately 60% and the auxiliary blower switch-on/off point, the turbocharger efficiency is relatively low and within this power range the engine operates with a lower air/fuel ratio resulting in higher exhaust gas temperatures.

The electronic controlled engines are more suitable for continuous low load operation than the conventional engines, due to their electronically  controlled common rail injection system.

Example of common rail injection system

These engines allow for higher injection pressure and selective fuel injector cut-off at very low loads, thus reducing excessive carbon deposits, exhaust gas economiser and turbocharger fouling.

The engine makers have issued a set of recommendations that should be observed, in order to limit the adverse affects of continuous low load operation as much as possible. The following needs to be in order:

    • The fuel injection valves should be in good working order.
    • When operating on HFO, the fuel viscosity required at the fuel pump inlet for conventional engines must be in the range of 13 to 17 cSt; for electronically controlled engines must be in the range 10 to 20 cSt. However, it is recommended to maintain the viscosity at the lower end of the range 13 to 17 cSt as specified in the engine operating manual, without exceeding 150°C at engine inlet. Sufficient trace heating of the fuel system on the engine must be ensured.
    • Keep the LT cooling water close to upper limit at 36°C in order to maintain the optimum scavenge air temperature and to minimize effects of possible cold corrosion.
    • For DF (dual fuel) engines operating in gas mode or (Low Sulphur) liquid fuels keep the LT cooling water set point at 25 °C to maintain a low (optimized) scavenge air temperature.
    • Clean the turbocharger as per manufacturer’s instruction manual.

Apart from above the following should be observed, monitored and adjusted accordingly:

    • The cylinder oil feed rate is load and sulphur dependent and is recommended to be properly adjusted as per the fuel that it is in use (about cylinder lubrication you can read in here). Frequent piston underside inspections must be carried out to monitor piston running conditions and signs of over-lubrication, as over-lubrication can lead to scuffing due to hard alkaline deposits on the piston crown.
    • The exhaust gas temperature after the cylinders should be kept above 250°C in order to reduce and avoid cold corrosion, fouling of exhaust gas receiver and turbocharger nozzle ring. If the exhaust gas temperature drops below this value, the engine load should be increased.
    • If the exhaust gas temperature gets too high (>450°C after cylinders), the auxiliary blower may be switched to “continuous running”. However, it has to be taken into account that not all auxiliary blowers and circuit breakers may be suitable for continuous running at electrical loads above nominal current.
    • Repeatedly switching on/off of the auxiliary blower must be avoided. If necessary, the auxiliary blower controls have to be switched to “manual operation”, or operation in this load area has to be avoided.
    • Inspect and lubricate the bearings more frequently if considered necessary due to increased operation of the blower. This also includes the inspections of the non-return valves for the scavenging air.
    • A concern during continuous low load operation is the accumulation of unburned fuel and lubricating oil in the exhaust manifold, as such deposits can ignite after the engine load is increased again. This may result in severe damage to the turbocharger due to sudden over-speeding. Therefore, it should be considered to periodically (twice a week) increase the engine load as high as possible, however at least 70% for at least 1 hour, in order to burn off accumulated carbon deposits. The load-up has to be done very carefully (i.e. during 2 hours) in order to avoid adverse piston running conditions due to carbon that has built up on the crown land of the piston head and to avoid possible exhaust manifold fire.
    • Exhaust manifold and other related components (scavenging air receiver, exhaust gas valves, turbocharger grid, etc.) need more frequent inspections and possible cleaning. Depending on result of inspections, the regular engine load-up intervals might be adapted if no excessive deposit accumulation is detected.
    • An economiser with closely-spaced fins may also require more frequent soot blowing.
    • On Dual-Fuel (DF) engines operating in gas mode, the described regular loading up to high loads is not required. The deposit formation is minimal compared to diesel mode operation.

In order to improve the piston running performance and reduce the risk of cold corrosion in cylinder liners, when the engine is continuously running at low loads, the temperature range of the cylinder cooling water outlet is increased. For example, Wärtsilä recommends keeping the cylinder cooling water outlet temperature as close as possible to the alarm limit. As a consequence of the increase of the cylinder cooling outlet water temperature, the respective alarm and slowdown settings need to be adjusted in some engines as well.

Example of alarm settings on Wartsila engines

In order to further optimize the engine operation at low load, Wärtsilä has developed A Slow Steaming Upgrade Kit that involves cutting out of a turbocharger.

Example of Wartsila Slow Steaming Kit

This increases the scavenge air delivery at low load for better combustion and more optimum temperatures of engine components. With this kit the following is achieved:

    • With the increased scavenge air pressure the auxiliary blower on/off threshold is at lower loads compared to engines with all turbochargers operative.
    • A considerable reduction in SFOC with cut out turbocharger and increased scavenge air pressure in the low-load range.
    • Due to better combustion at lower loads the risk of turbocharger and economizer fouling is decreased and the formation of deposits due to unburnt fuel is reduced.

The time interval between engine load-up to burn off carbon deposits can be increased based on inspection results. In order to burn off the deposits, a high enough exhaust gas temperature at turbine inlet is needed. The engine needs to be loaded up until the exhaust gas temperature at turbine inlet corresponds to 380°C. If this temperature is not possible to reach, the engine needs to be loaded up to the maximum load that can be reached with one turbocharger cut-out.

In combination with the above described slow steaming kit, Wärtsilä also recommends the installation of electronically controlled cylinder lubrication, called Retrofit Pulse Lubrication System which provides optimal lubrication due to the precisely timed feeding of oil into the piston ring pack and savings in lubricating oil.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries.

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Source and Bibliography:

  • Wartsila 2 Stroke –  Service letter RT174 – 27/11/2014

What is VIT + FQS?

VIT or Variable Injection Timing is a form of fuel pump control, enabling an engine to operate with the designated maximum cylinder firing or combustion pressure from approximately 75% power output to maximum power. This improves thermal efficiency and lowers fuel consumption.

The fuel consumption for an engine at any load will be related to the expansion ratio of the combustion gases from their maximum pressure to the pressure at the commencement of exhaust blowdown.

The maximum cylinder pressure is a factor used in the design of the crankshaft and other important engine parts. In a normal engine the maximum cylinder pressure is reached only at full power operation, whereas with VIT the maximum cylinder pressure is reached at about 75% of the full load. The expansion ratio is therefore increased when the engine is operating under light loads right up to full load.

Variable beginning of injection

When the engine is equipped with a VIT+FQS system (Variable Injection Timing + Fuel Quality Setting) which permits an alteration of injection begin during operation, the system produces a maximum firing pressure over a wide power range close to the value for the Contracted
Maximum Continuous Rating (CMCR) and thereby reduces the fuel consumption. It is also possible to tune the VIT+FQS system following NOx emission. In this case the VIT angle is reduced and thereby the injection is retarded over a wide load range in order to reduce NOx emission.

Generally is used the indication VIT+FQS because VIT and FQS always act together, unless the data is specified only for VIT or only for FQS. The VIT+FQS control is integrated in the engine remote control and under normal operating conditions the VIT function is always on, but it can be switched off whereupon the actuator moves to the position corresponding to the FQS setting.

In its normal operating mode the VIT+FQS system produces earlier injection in the partial power range and therefore raises the maximum firing pressure. The standard VIT program calculates the necessary VIT angle for increased part load using scavenge air pressure and engine speed as input signals and therefore, a reduction of the fuel consumption is effected over the entire load range. The standard VIT program is individually adjusted during the shop trial of the engine. A typical curve can be seen on below diagram.

Electronic VIT and FQS unit

With the aid of a pneumatic cylinder and a mechanical linkage the suction valve and spill valve regulating are simultaneously altered. For example, the moving out of the pneumatic cylinder gives higher VIT angles, i.e. an earlier injection and therefore a higher maximum firing pressure.

Sectional view of Sulzer RTA fuel pump
Sulzer RTA VIT pneumatic cylinder
Sulzer RTA VIT indicator

With the manual adjustment of FQS, the influence of fuel quality is compensated. Fuels having a low ignition quality result in lower firing pressures for the same start of injection, i.e. for compensation, the FQS angle has to be increased. Fuels with better ignition quality result in higher firing pressure for the same start of injection, i.e. for compensation, the FQS angle has to be reduced.
For this purpose the FQS angle is defined as ’user parameter’ in the engine control and can be adjusted within the range of –3 deg. to +3 deg. The manual FQS adjustment supposes a firing pressure measurement before and after and it must further be established whether the firing pressure alteration is actually due to a fuel quality change. Alteration of firing pressure due to fouling or other causes may not be compensated with the FQS adjustment.

Into below videos you can learn on how the fuel pump’s injection timing can be adjusted on different type of engines

MAN Diesel fuel injection timing adjustment
Sulzer RTA fuel injection timing adjustment

In the electronically controlled engines, the control of fuel injection is based upon volumetric injection control. Each cylinder electronic unit calculates the necessary injection timing for its own cylinder by processing the crank angle signal and the fuel command delivered by the master control module (MCM).

In these cases there is no need for adjustment as the VIT angle calculation depends on speed (RPM), charge air pressure and the fuel rail pressure. The (new) fuel rail pressure compensates for the differences in injection timing resulting from different fuel injection pressures in the fuel rail. Higher fuel pressure causes advanced injection and higher maximum pressure (Pmax). Thus the injection start angle is retarded by a small amount with increasing fuel rail pressure.

In conclusion, in order to run the engine efficiently and to avoid engine breakdowns and damage, proper maintenance and periodical checks must be carried out as per your company and manufacturer’s maintenance plan and instructions. Moreover, every engineer must be familiar with proper monitoring and how to take engine performance cards and how to properly adjust the fuel pump’s timing.

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