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Enhancing Marine Engine Efficiency: A Solution for Low-Speed Operation

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Author: Daniel G. Teleoaca – Marine Chief Engineer

Marine engines are the unsung heroes of the shipping industry, tirelessly powering vessels across vast oceans and seas.

However, these workhorses face a unique challenge when it comes to low-speed operation. Low speed operation can cause various problems for marine engines, such as increased fuel consumption, reduced power output, higher emissions, and more wear and tear. The inefficiency of marine engines at lower speeds can have significant economic and environmental implications.

Preceding the implementation of emission-limiting regulations, some of the ships, especially containers, were generally engineered to achieve maximum cruising velocities of 30 knots. Presently, operators are obligated to comply with regulatory frameworks such as the carbon intensity indicator (CII) and the energy efficiency existing ship index (EEXI).

As a consequence, cruising veers off at approximately 18 knots, which is roughly two-thirds the speed for which the engines were originally designed. As a result, engines operate extremely inefficiently at low loads, consuming significantly more fuel and emitting significantly more CO2 than is required.

Without intervention, Wartsila predicted in 2022 that by 2023, over one-third of container ships would be non-compliant, based on an analysis of the global fleet. Moreover, in the absence of intervention, 80% of container ships will be classified under the lowest CII category by 2030.

In this article, we’ll explore the reasons behind this inefficiency and the options available to improve marine engine performance when running at low speeds.

Understanding the Inefficiency

Marine engines are designed to operate at a certain range of speed and load, depending on the type and size of the engine, the ship’s hull form, the propeller characteristics, and the operating conditions. When the engine operates outside this range, it can suffer from inefficiency and performance loss. There are several key reasons for this inefficiency:

  • Reduced Combustion Efficiency: A cause of marine engine inefficiency at low speed is the incomplete combustion of fuel in the cylinders. The combustion process in a marine engine depends on many factors, such as the fuel quality, the air-fuel ratio, the injection timing, the compression pressure, the ignition temperature, and the combustion duration. When the engine operates at low speed and load, some of these factors can be adversely affected, resulting in incomplete combustion of fuel. Incomplete combustion can lead to lower power output, higher fuel consumption, higher emissions of carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), and smoke, and more carbon deposits in the cylinders and turbocharger.

  • Mechanical Losses: At low speeds, the engine’s mechanical components, such as pistons, bearings, and crankshafts, experience higher frictional losses. This additional resistance leads to decreased engine efficiency. Moreover, the turbocharger is a device that uses the exhaust gas from the engine to drive a compressor that increases the air pressure and density in the intake manifold. The turbocharger improves the engine performance by allowing more air and fuel to be burned in each cylinder. The turbocharger efficiency depends on the pressure ratio between the exhaust gas and the intake air, which is called the boost pressure. The boost pressure is highest at high engine speed and load, when there is more exhaust gas available to drive the turbocharger. When the engine operates at low speed and load, there is less exhaust gas available, and the boost pressure drops. This means that less air is supplied to the cylinders, resulting in lower power output, higher fuel consumption, higher emissions of nitrogen oxides (NOx), and more turbo lag.

  • Propeller Inefficiency: One of the main causes of marine engine inefficiency at low speed is the mismatch between the engine and the propeller. The propeller is a device that converts the rotational energy of the engine into thrust force for propulsion. The propeller efficiency depends on the ratio of the propeller speed to the ship speed, which is called the advance ratio. The propeller efficiency is highest at a certain advance ratio, which corresponds to a certain engine speed and load. When the ship operates at low speed, the advance ratio increases, and the propeller efficiency decreases. This means that more engine power is wasted as friction and turbulence in the water, rather than converted into useful thrust.

Therefore, the effects of marine engine inefficiency at low speed can be summarized as follows:

  • Lower power output: The engine produces less power than it is capable of, resulting in lower ship speed or lower reserve power for maneuvering or emergency situations.
  • Higher fuel consumption: The engine consumes more fuel than it needs to produce a given amount of power, resulting in higher operating costs and lower profitability.
  • Higher emissions: The engine emits more pollutants than it should, resulting in environmental damage and potential non-compliance with emission regulations.
  • More wear and tear: The engine suffers from more stress and damage due to friction, corrosion, erosion, vibration, overheating, fouling, etc., resulting in higher maintenance costs and lower reliability.

Options to improve marine engine efficiency and performance at low speed

The inefficiency of marine engines at low speeds is a persistent challenge, but there are several innovative solutions available to mitigate this issue. Some of these options are:

  • Variable Geometry Turbochargers (VGTs): VGTs are turbochargers that can adjust their geometry to optimize airflow at different engine speeds. They help maintain higher combustion efficiency, even at low speeds, reducing fuel consumption and emissions.

  • Slow Steaming Strategies: Slow steaming involves deliberately operating a vessel at reduced speeds to conserve fuel. It has become a popular strategy in the shipping industry, allowing ships to run more efficiently at lower RPMs, thus saving fuel.

  • Dual-Fuel Engines: Dual-fuel engines are designed to run on a combination of natural gas and diesel fuel. These engines offer improved combustion efficiency and emissions control, making them an attractive option for low-speed operation.

  • Waste Heat Recovery Systems: Waste heat recovery systems capture and reuse the heat generated by the engine’s exhaust. They can be used to produce additional power or drive other ship systems, enhancing overall energy efficiency.

  • Upgraded Propellers: Shipowners can consider investing in more efficient propeller designs, specifically tailored to their vessels’ operating profiles. Modern propeller designs are more adaptable to a wide range of ship speeds.

  • Improved Hull Design: The vessel’s hull design can also impact its performance at lower speeds. Optimized hull shapes can reduce hydrodynamic resistance and improve overall efficiency.

  • Hybrid Power Systems: Some vessels employ hybrid power systems that combine traditional diesel engines with electric propulsion. This setup allows for efficient power delivery at various speeds, including low-speed operation.

  • Engine derating: Engine derating is a method of reducing the maximum power output of an engine by adjusting its settings or components. Engine derating can improve the engine efficiency at low speed by reducing the mismatch between the engine and the propeller, and by optimizing the combustion process and the turbocharger operation. Engine derating can also reduce the emissions of NOx, CO, HC, and PM. However, engine derating can also reduce the reserve power of the engine, and may require the approval of the engine manufacturer and the classification society.
  • Turbocharger cut-out: Turbocharger cut-out is a method of disconnecting one or more turbochargers from an engine by closing a valve or opening a bypass. Turbocharger cut-out can improve the engine efficiency at low speed by increasing the boost pressure and the air supply to the cylinders. Turbocharger cut-out can also reduce the emissions of CO, HC, and smoke. However, turbocharger cut-out can also increase the emissions of NOx, and may cause the turbocharger to overheat or surge.

In conclusion, addressing the inefficiency of marine engines at low speeds is critical for both economic and environmental reasons. The shipping industry has made significant strides in developing technologies and strategies to improve engine efficiency during slow steaming and low-speed operation. These solutions not only reduce fuel consumption but also contribute to lower emissions and a more sustainable maritime industry. As technology continues to advance, marine engines are likely to become more versatile, making them more efficient across a broader range of operating speeds, ultimately benefiting the entire global shipping industry.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World, Telegram Chief Engineer’s Log Chat or Instagram and will try to answer to all your queries. You can use the feedback button as well!

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

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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.

If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!

Source and Bibliography:

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

What you need to know about 4-stroke engine turbocharger wet and dry cleaning

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Operational experience has shown that 4 stroke engines operating heavy fuels being bunkered from various ports globally and low load operation of the engine tend to cause fouling of the turbocharger.

The condition and cleanness of the turbine of an exhaust -gas turbocharger have a decisive influence on the efficiency, the performance of the combustion process and hence on the service data of the engine which will be negatively affected.

Possible consequences can be, but not limited to:

      • overspeed of the turbine
      • vibration excitation of the turbine caused by deposits
      • reduced engine efficiency
      • increased fuel consumption

Fouling of the turbine side of the turbocharger will, in its first phase, manifest itself in increasing turbocharger revolutions on account of increased gas velocity through the narrowed nozzle ring area. In the long run, the charging air quantity will decrease on account of the greater flow resistance through the nozzle ring, resulting in higher wall temperatures in the combustion chambers.

Example of turbocharger nozzle ring fouling

A high contamination level with deposits will cause an offset to the normal gas flow resulting in increase in temperature level before the turbine or in extreme case cause surging. This can lead to significant increase in unfavorable excitation orders of vibration which could advance a severe damage of the turbocharger by causing fatigue on the turbine rotor vanes.

Service experience has shown that the turbine side is exposed to increased  fouling when operating on HFO.

The rate of fouling and thereby the influence on the operation of the engine is greatest for small turbochargers where the flow openings between the guide vanes of the nozzle ring are relatively small. Deposits occur especially on the guide vanes of the nozzle ring and on the rotor blades.

In accordance with the operating conditions of the engine, it is sometimes necessary to free both nozzle ring and the blading of the turbine from deposits and other adhesive particles from the combustion process.
This mechanical cleaning is normally carried out in the course of the specified maintenance intervals (general turbocharger overhaul). The turbine rotor and nozzle ring of the turbocharger have to be dismantled for the cleaning process.

Example of turbocharger impeller opened for overhaul

Turbine side of the turbocharger can be cleaned effectively by combination of wet water washing and dry nut shell cleaning, hence it is recommended to carry out wet as well as dry cleaning of turbochargers.

Wet cleaning of the turbines during low-load engine operation has been used for a long time in order to achieve the specified time intervals between the turbocharger inspections and to protract the time-consuming manual cleaning of turbine and nozzle ring.
Wet cleaning is normally carried out about every 250 hours, but it can be executed in shorter or longer intervals depending on the operating conditions. Regular performance observations will show the trend in charge air pressure and exhaust gas temperatures, and define the cleaning intervals for the turbine.
To carry out the wet cleaning process, the engine load has to be significantly reduced and the exhaust gas temperatures have to be put into steady-state condition. The preparation and execution of the wet cleaning process easily adds up to approx. 1 hour during which the full engine load is not available.

The wet cleaning tool would be connected to the same connection as dry cleaning, through a snap coupling.

Example of TC washing connection arrangement

As all injected water is not evaporated, turbochargers need to be fitted with a drain from the exhaust gas outlet. The necessary water flow is dependent on exhaust gas flow and temperature and must be so high that all water does not evaporate, also the water flow must not be so high that the turbine wheel is drowned and stops rotating. The washing sequence should be in accordance with turbocharger manual and the engine load, exhaust gas temperature before turbine and the turbine speed must be as per same manual.

Example of T/C wet and dry cleaning tools

The wet washing kit comes with different nozzle orifice which should be choose as per engine size. If you want and are interested for more in depth information regarding nozzle selection and water flow adjustment  you need to subscribe to Seafarer’s World Forum (powered by chiefengineerlog.com).

The dry cleaning of the turbine is carried out by blowing in granulate (nutshells or activated charcoal) of a specified particle size and volume – the volume depends on the turbocharger type – into the exhaust pipe before turbine under operating load by means of compressed air and permanently attached nozzles. The high kinetic energy produced during the impact of the granulate onto the nozzle ring and turbine blading causes the deposits to flake off. It is not necessary to reduce the engine load for the cleaning process. If you want and are interested for more in depth information regarding procedure and flow adjustment you need to subscribe to Seafarer’s World Forum (powered by chiefengineerlog.com).

Practical experiences gained over the years have shown that the intervals of wet cleaning can be extended when using the dry cleaning system.
It also became apparent that the increase of the cleaning interval for dry cleaning – from once a day to twice a day – results in a significant improvement of the cleaning result when using highly coating -forming heavy oil fuels.

Example of TC before and after cleaning

Benefits of dry cleaning compared with wet cleaning:

      • turbine can be cleaned at full load – thus no losses at all in the operational readiness of the engine;
      • short execution time of the cleaning procedure (approx. 20 min);
      • frequent use of the cleaning process effectively prevents deposits at nozzle ring and turbine blades

If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!

Diesel engine troubleshooting and diagnostic

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Every ship’s engine room is equipped with some kind of diesel engine and most big ships nowadays are powered by two-stroke diesel engines, although the usage of four-stroke engines for propulsion is increasing due to the flexibility in where they may be installed and the enhanced redundancy that a larger number of smaller engines can give. Four stroke diesel engines are commonly utilized to generate electricity.
Diesel engine troubleshooting or diagnosis is a tool that should help ensure the diesel engine’s dependability as well as its maximum efficiency, to prevent severe problems at sea and to have condition-based maintenance and be possible to assess the technical state of the engine sections without disassembling the engine.
Engine monitoring can be thought of as a simpler diagnosis that follows this simple rule: as long as the vital engine parameters are within a particular range, we can conclude that a critical defect is not imminent. However, such basic monitoring does not help striving for optimal engine efficiency or maintenance optimization and as a result, a more complete troubleshooting can be extremely beneficial.

The values of the engine parameters are affected by both the engine’s condition and the operating conditions (e.g. ambient elements such as draught, sea water status, air pressure, and temperatures, as well as selectable criteria such as demanded ship speed or specified electrical load). As a result, we must compare the values of diagnostic parameters not merely with their prior values, but also with the reference values obtained from the sea trial data, also known as model diagrams.

Because we can use different settings to analyze different engine components, different conditions should be used as independent variables for distinct troubleshooting and diagnostic metrics and model diagrams are typically based on the findings of sea trials or test beds.

The best troubleshooting and diagnosis parameters to use are measured engine values that meet the following criteria:

    • their value is dependent not only on operating conditions but also, to a large extent, on the technical state of the engine;
    • they assist us in avoiding the most serious faults;
    • they assist us in optimizing the maintenance process;
    • they can be measured using the engine equipment that is available.

Load index, engine torque, engine rpm and power and fuel specific consumption, calculated over a long enough period of time, are the troubleshooting and diagnostic measures most typically used for evaluating engine performance.

Engine overload is commonly produced by attempting to sail the ship through severe seas while setting the requested engine rpm to a high value. Usually, engine overload is frequently detected by the engine monitoring system, however regular monitoring of the operating point position is required to avoid such a problem.

Because fuel consumption varies with engine load, we must first compare the actual value with the model diagram value for the same engine power to develop a trend in Specific Fuel Consumption (SFOC). We can then display the deviation over time, most likely weeks, because some external influences, such as tide or weather conditions, may affect individual observations in the long run. If the SFOC is higher, it indicates that the total engine efficiency is worse, which should prompt more troubleshooting to determine the problem.

Engine vibrations are common, especially when starting the engine or sailing in rough waves. The majority of engine issues fall into two categories: combustion faults and mechanical faults.

The combustion defects, vibration-based condition monitoring may be further classified into two types: one is based on translational acceleration signals detected on the engine block or cylinder tightening bolts, and the other is based on torsional vibration signals produced from the torque meter. It is normally important to have data analysis software in order to use these signals. Even still, problems cannot always be detected automatically based on the studied vibration signals. As a result, any divergence should prompt a new search to pinpoint the specific cause of the issue.

Example of engine vibration diagram

At its most basic, the frequency vibrations are usually the most telling indicator of where the flaws are located, as the vibrations will have the same frequency or components with frequencies multiples of the frequency of the faulty portion. For example, very high frequency vibrations are most often caused by high speed components such as those found in turbochargers. The shafting system is commonly linked with very low vibrations.

Indicator diagrams, mean indicated pressure, exhaust gas temperature after each cylinder, compression pressure in each cylinder and maximum pressure in each cylinder are the troubleshooting and diagnostic metrics used to evaluate combustion.

The most common engine combustion symptoms include:

    • Dark smoke from the funnel
  • Dark smoke from the funnel usually indicates a lack of combustion air and it can appear when the engine starts, during a sudden load increase (e.g. during maneuvering and in rough seas due to abnormal engine loads). A failure in the turbocharging system might create dark smoke under constant engine loads.

    • An increase in the positive deviation of the mean exhaust gas temperature
  • The first stage in analyzing exhaust gas temperatures is to compare the actual value of the average exhaust temperature with the average value from the model diagram for the same engine power. The following issues can cause an increasing positive deviation of the average exhaust gas temperature:
        • high inlet temperature of the cylinder cooling water;
        • low inlet pressure of the cylinder cooling water;
        • high inlet temperature of the oil cooling the pistons;
        • low inlet pressure of the oil cooling the pistons;
        • insufficient combustion air.
    • An increase in the deviation of the exhaust gas temperature after a single cylinder
  • The first stage in analyzing exhaust gas temperatures after each cylinder is to compare the actual value to the average exhaust temperature after all cylinders at the same time.  Some variances in exhaust temperatures between units may be normal, but increases in detected deviations indicate that something has occurred and can be used to troubleshoot engine conditions. The following issues can cause an increasing positive variance in exhaust gas temperature after a single cylinder:
        • late combustion, caused by the wrong injection timing or by worn fuel injector valve, which can be identified using an indicator diagram;
        • a leaking exhaust valve, which can be identified by an increasing negative deviation of the compression pressure.
    • An increase in the negative deviation of the compression pressure in a single cylinder
  • When evaluating the compression pressure in a cylinder, compare the actual value of the compression pressure with the value from the model diagram for the same scavenge air pressure.
    The following issues, which are normally visible during a scavenging port examination, might cause a growing negative deviation of the compression pressure in a cylinder:

        • blocked cylinder inlet ports;
        • wear of the piston rings or the cylinder;
        • clogged or burned out piston rings.
    • An increase in the negative deviation of the maximum combustion pressure in a single cylinder
  • Compare the actual maximum combustion pressure in each cylinder to the average maximum combustion pressure in all cylinders at the same time when evaluating the maximum combustion pressure in each cylinder. Some variation in maximum combustion pressure between units is usual.
    An increasing negative deviation of the cylinder maximum combustion pressure can be caused by the following issues:

        • a low compression pressure, which should be eliminated first as previously described;

      • Example of low combustion pressure due low compression pressure

        • delayed combustion, which can be caused by incorrect injection timing or worn injection nozzles (this problem can be observed on the indicator diagram);

      • Example of low combustion due wrong timing

        • a decreased quantity of fuel injected, which can be caused by a worn plunger in the fuel pump (this can be confirmed by checking the Mean Indicated Pressure ) and if this is the cause the pump should be overhauled.
    • An increase in the negative deviation of the Mean Indicated Pressure, M.I.P. in a single cylinder or group of cylinders

The following diagnostic parameters are used to evaluate a turbocharger:  turbocharger rpm, exhaust temperature before and after the turbocharger, scavenge air pressure, air pressure drop at the air filter, air pressure drop at the air cooler, exhaust pressure after the turbocharger (also known as the counter-pressure) and the cooling water temperature difference at the air cooler.

The typical symptoms of turbocharging problems are:

    • Increased negative deviation of the scavenge air pressure

The following issues can cause an increasing negative divergence in scavenging air pressure:

        • a clogged air filter (which should be replaced first);
        • a malfunctioning or dirty turbocharger;
        • a clogged exhaust duct after the engine, which can be found by measuring the exhaust pressure after the turbocharger.
    • Increasing deviation of the turbocharger speed (positive or negative)

A corroded turbocharger nozzle ring or turbine blades, an excessive clearance between the turbine blades and the shroud or cover can all cause an increase in negative turbocharger speed deviation. As a result, on the model diagram, turbocharger speed should be referred to the scavenging air pressure.
The following issues can cause an increasing positive divergence in turbocharger speed:

        • a dirty air filter;
        • a dirty air cooler;
        • a dirty turbocharger, either air or gas side, which should be removed by washing both sides according to the manufacturer’s instructions.
    • Increasing positive deviation of the air pressure drop at the air filter

When assessing the air pressure decrease at the air filter, start by comparing the actual value to the value from the model diagram for the same scavenging air pressure. A dirty air filter, which should be cleaned according to the manufacturer’s instructions, might produce a rising positive deviation of the air pressure drop at the air filter.

View of turbocharger air filter

    • Increasing positive deviation of the air pressure drop at the air cooler

When assessing the air pressure drop at the air cooler, start by comparing the actual value to the value from the model diagram for the same scavenging air pressure. A dirty air side of the air cooler, which should be cleaned according to the engine manual, can cause an increasing positive deviation of the air pressure drop at the air cooler.

    • Increasing negative deviation of the cooling water temperature at the air cooler
  • A dirty water side of the air cooler, which should be cleaned according to the engine handbook, can create a growing negative deviation of the cooling water temperature differential.
    • Increasing cylinder block temperature near the scavenge box

The temperature of the cylinder block surface near the scavenge box should be assessed using an infrared camera or measured by placing the palm of the hand close to, but without touching, the cylinder block and comparing it to other cylinders. A rising cylinder block temperature near the scavenge box, particularly when accompanied with rising exhaust gas and cooling water temperatures, can be a sign of a scavenge box fire. This type of fire is frequently caused by worn piston rings or an overabundance of cylinder oil. When a scavenge box fire is detected, the engine load should be quickly reduced and a fire extinguishing method (CO2, steam, etc.) should be used in accordance with the engine manual.

The following diagnostic metrics are used to evaluate engine cooling: cooling water temperature after each cylinder, cooling water temperature at the engine’s inlet and piston cooling oil temperature at the engine’s inlet.

An rising positive deviation of the cooling water temperature difference at the cylinder is a common indicator of an engine problem.

When assessing the cooling water temperature differential at the cylinder, start by comparing the actual value to the value from the model diagram for the same engine power. Several problems can cause an increasing positive deviation of the cooling water temperature difference at a cylinder:

      • a crack in the cylinder liner (which can be accompanied by bubbles in the cooling water expansion tank);
      • a crack in the cylinder head (which can be accompanied by bubbles in the cooling water expansion tank);
      • an obstacle in the cylinder liner or the cylinder head cooling space (in this case there are no bubbles in the cooling water expansion tank).

Piece of rag found inside cooling pipe

 

The diagnostic parameters utilized for engine lubrication evaluation are: main bearing temperatures (if available), lubricating oil temperature before the engine, lubricating oil water content, lubricating oil pH and lubricating oil viscosity.

The typical signs of an engine lubrication problem are:

  • Increased positive deviation of the main bearing temperatures

The temperature of each main bearing should be compared to the limiting value, and an alert should be generated when it reaches the limit, which depends on both the main bearing material and the placement of the temperature sensor.

All possible causes of an increased positive deviation of the main bearing temperature are:

        • A seizure process in the bearing, which can be caused by material failure, a sudden load increase, or obstructed oil flow;
        • An obstructed flow in the crankshaft drilling caused by lubrication oil impurities;
        • A cylinder mechanical overload caused by an excessively high maximum combustion pressure;
        • Bearing corrosion

A main bearing seizure can result in the bearing’s disintegration and a main engine emergency stop.

Example of main bearing failure

  • High water content in the lubricating oil

The water content can be measured on-board with special equipment, but it can also be monitored continuously by a sensor fitted in the lubricating oil inlet line.

Example of water in oil tester

A rising water content in the lubricating oil can be caused by a number of issues, including:

        • insufficient or faulty operation of the lubricating oil separator;
        • a cooling water leak into the cylinder due to a crack in the cylinder liner or cylinder head;

      • Exampled of cracked cylinder liner

        Crank in cylinder head

 

 

 

 

 

 

        • excessive water condensation in the charge air after the cooler (this usually occurs when humidity is high and the scavenge air temperature is low, allowing the dew point to be reached). This can be verified by opening the scavenge box’s drain valve); a worn or broken stuffing box can allow water to seep from the scavenge box into the engine crankcase.

Lubricating oil with a high water concentration can cause bearing corrosion, inadequate lubrication, and bearing seizures.

  • Low pH of the lubricating oil

The pH of the lubricant oil can be measured aboard using pH test strips.

Example of pH test strips

A low pH of the lubricating oil can be caused by a number of issues, including an increased amount of acidic combustion products due to a high sulphur content in the fuel or a low TBN of the cylinder oil and a worn or broken stuffing box, which allows combustion products to enter the engine crankcase.

Low lubricating oil pH is a severe issue since it can cause bearing corrosion.

  • Low viscosity of the lubricating oil

Onboard, the viscosity of lubrication oil is determined by comparing the oil flow speed with a flow stick.

Example of a viscosity testing flow stick

A low viscosity of the lubricating oil can be caused by several issues, including:

        • unburned fuel oil leaking past the piston rings to the stuffing box and further into the crankcase through an untighten stuffing box;
        • contamination with fuel oil from fuel pump lubrication;
        • a high water content in the lubricating oil;
        • oil deterioration due to age or contamination.

Lubricating oil with a low viscosity can cause significant engine damage.

  • High contamination, or low dispersancy, of the lubricating oil

A spot test can be used to check for contamination and dispersancy in lubricating oil.

Example of a spot test used onboard

A drop of oil is placed on blotter paper and dried for a few hours in this test. The dry spot is then compared to the available example spots, allowing the insoluble components in the oil to be determined.
Lubricating oil contamination is typically caused by poor oil filtering or insufficient cleaning in the lubrication oil separator and oil contaminants can clog oil flow in small clearances and disrupt hydrodynamic lubrication.
The ageing of the oil usually causes low dispersancy of the lubricating oil. Lubricating oil dispersancy is required to separate larger size deposits into microscopic particles that may then be transported uniformly throughout the majority of the oil and afterwards removed by filtering.

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