Tag Archives: main engines

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.

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The Importance of Air Seals on Main Engine Exhaust Valves

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In the world of engineering and machinery, precision and reliability are paramount. One critical component that plays a vital role in ensuring the efficiency and performance of a combustion engine is the exhaust valve. To optimize the functioning of this crucial part, engineers have developed air seals that help maintain a secure and efficient seal. In this blog post, we will explore the significance of air seals on main engine exhaust valves, the types of air seals used, and their role in enhancing engine performance.

The Main Engine Exhaust Valve: A Crucial Component

Before diving into the intricacies of air seals, it’s essential to understand the importance of the main engine exhaust valve in a combustion engine. In an internal combustion engine, whether it’s found in a car, a ship, or an industrial machine, the exhaust valve serves a fundamental purpose. The main engine exhaust valve is a vital component of a marine diesel engine that controls the timing and duration of the exhaust gas flow from the cylinder to the turbocharger. The exhaust valve consists of several parts, such as the spindle, the housing, the seat, the hydraulic cylinder, and the air cylinder. The air cylinder is a device that uses compressed air to close the exhaust valve against the hydraulic pressure that opens it. The air cylinder has a piston that moves up and down along with the spindle, creating an air spring effect that ensures a smooth and reliable operation of the exhaust valve.

The Challenge: Gas Leakage

One of the primary challenges in designing exhaust valves is preventing gas leakage. Inefficient sealing can lead to several adverse consequences, including:

  • Reduced Efficiency: Gas leakage results in a loss of engine efficiency, as the engine must work harder to compensate for the escaping exhaust gases.
  • Environmental Impact: Incomplete combustion due to gas leakage can lead to increased emissions, contributing to air pollution and environmental degradation.
  • Increased Fuel Consumption: Gas leakage forces the engine to burn more fuel to maintain power output, leading to higher operational costs.

Types of Air Seals

To address the issue of gas leakage, engineers have developed various types of air seals, each with its own unique characteristics and applications. The air seal is a device that prevents air leakage from the air cylinder to the exhaust valve housing. It is made of a metallic outer ring and a rubber seal that contacts the spindle. The seal can have different shapes depending on the type of valve. The air seal is important for maintaining the proper air pressure and spring force in the air cylinder, as well as for protecting the spindle from corrosion and fouling by the exhaust gas. A faulty or worn-out air seal can cause air loss, reduced performance, increased fuel consumption, and higher emissions.

Exhaust valve air piston seal ring overhaul. Source and Credit: Rheinstinitz Karl Caler

Here are some common types of air seals used in main engine exhaust valves:

  • Floating Ring Seals: Floating ring seals consist of two concentric rings, with the outer ring rotating along with the valve. This design helps create a dynamic seal, minimizing gas leakage.
  • Poppet Valve Seals: Poppet valves are commonly used in internal combustion engines. They employ a cylindrical plug to control gas flow. Air seals in poppet valves help ensure a tight fit between the valve and the valve seat, preventing gas leakage.
  • Rotary Valve Seals: Rotary valves, found in some engines like rotary engines and two-stroke engines, use rotary seals to maintain a seal as the valve rotates. These seals play a crucial role in preventing gas leakage.
  • Labyrinth Seals: Labyrinth seals consist of intricate channels and ridges that create a tortuous path for gas to escape. This design effectively reduces gas leakage by increasing the distance exhaust gases must travel before exiting.

The Role of Air Seals in Enhancing Engine Performance

Air seals on main engine exhaust valves are vital for several reasons:

  • Gas Tightness: The primary function of air seals is to maintain gas tightness within the combustion chamber. This ensures that exhaust gases exit through the designated path, optimizing engine efficiency.
  • Reduced Emissions: By minimizing gas leakage, air seals contribute to lower emissions. This is especially critical in modern engines to meet stringent environmental regulations.
  • Improved Fuel Efficiency: A well-sealed exhaust valve reduces the engine’s workload, leading to improved fuel efficiency and reduced operational costs.
  • Enhanced Engine Longevity: Air seals help protect the engine from excessive wear and tear, prolonging its operational life.

The air seal on the main engine exhaust valve is a simple but important device that ensures efficient and safe operation of the engine. Therefore, it is essential to inspect and replace the air seal regularly as per the maker’s recommendations.

Example of exhaust valve overhauling. Source and Credit: DG E LEARING ADU ACADEMY

In conclusion, in the intricate world of internal combustion engines, even the smallest components play a critical role in ensuring performance and efficiency. Air seals on main engine exhaust valves are a testament to the precision and engineering prowess required to design and maintain these complex machines. By preventing gas leakage, these seals contribute to reduced emissions, improved fuel efficiency, and increased engine longevity. As technology continues to advance, we can expect further innovations in air seal designs, driving the continuous improvement of combustion engines in various applications.

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The Necessity of Cutting Out One of the Vessel’s Main Engine Unit: A Comprehensive Guide for Marine Engineers

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Maintaining the efficient and safe operation of a vessel’s main engine units is crucial for smooth sailing and ensuring the safety of all onboard. In certain circumstances, it becomes necessary to cut out the combustion on or to isolate one of the main engine units. This article will delve into the process of cutting out combustion and isolating the unit, discuss when it is necessary, highlight the factors marine engineers need to consider, and outline the essential precautions and measures to be taken. The extent of the work to be carried out depends, of course, on the nature of the trouble.

Understanding the Process of Cutting Out Combustion

When a marine engineer decides to cut out the combustion on a main engine unit, it means intentionally stopping the fuel injection into that particular unit. By doing so, the engine’s power output is reduced, and it ceases to contribute to the propulsion of the vessel. This process involves a systematic and controlled approach to ensure the safety and functionality of the remaining operational units.

When is it Necessary to Cut Out Injection on a Main Engine Unit?

There are several scenarios in which cutting out the injection on a main engine unit becomes necessary:

    • Technical Malfunctions: In the event of a malfunction or breakdown in one of the main engine units, cutting out the combustion allows the crew to isolate the faulty unit and prevent further damage. This ensures the vessel can continue its operations with the remaining functional engines. The technical malfunctions can be, for instance but not reduced to:
      • blow-by at piston rings or exhaust valve
      • bearing failures which necessitate reduction of bearing load
      • faults in the injection system.
    • Maintenance and Repairs: Routine maintenance and repair activities may require cutting out the combustion on a main engine unit. This allows the marine engineer to safely conduct necessary maintenance procedures, such as inspections, replacements, or repairs, without endangering the crew or vessel.
    • Fuel Economy and Efficiency: During periods of reduced power demand, such as when sailing at lower speeds or in calm waters, cutting out the combustion on one or more engine units can optimize fuel consumption and increase overall efficiency. This strategy helps minimize operating costs and extend the lifespan of the engines.

Process of Cutting Out Combustion on a Main Engine Unit

    • Initial Assessment: The marine engineer must conduct a thorough assessment of the engine to identify the specific unit requiring combustion cut-out. This includes analyzing performance data, monitoring alarm systems, and conducting visual inspections.

    • Preparing the Engine: Prior to cutting out combustion, the engineer needs to ensure the vessel is at a safe operating condition. This involves reducing the load on the affected unit and synchronizing the remaining engines, if required, for optimal performance.

    • Shutting Down Injection: Once the engine is prepared, the marine engineer can proceed with cutting out the injection on the designated unit. This is typically achieved by isolating the fuel supply, closing relevant valves, and activating the engine control system to cease fuel injection.

In case of camshaft type engine the injection can be cut out by lifting and securing the fuel pump roller guide. The entire procedure for cutting out the injection on one of the units is fully described in the engine manual.

Should the engine be kept running with the injection cut out for an extended period, the lubricating oil feed rate for the respective cylinder must be reduced to the minimum. If the piston and exhaust valve gear are still operational, do not shut down the piston cooling oil and cylinder cooling water on that particular unit.

In case of electronic controlled engines, cutting out the injection is more simpler as everything is done from the Engine Control Panel Unit.

You must be aware that with an injection pump cut out the engine can no longer be run at its full power.

Process of Combustion and Compression cut out. Piston still working in cylinder.

This measure is permitted in the event of, for instance, water is leaking into the cylinder from the cooling jacket/liner or cylinder cover.

The procedure is as follow:

    • Cut out the fuel pump by lifting and securing the roller guide.
    • Put the exhaust valve out of action and lock it in open position.
    • Shut-off the air supply to the exhaust valve, and stop the lube oil pumps. Dismantle and block the actuator oil pipe. Restart the lube oil pumps.
    • Close the cooling water inlet and outlet valves for the cylinder. If necessary, drain the cooling water spaces completely.
    • Dismantle the starting air pipe, and blank off the main pipe and the control air pipe for the pertaining cylinder.
    • When operating in this manner, the speed should not exceed 55% of MCR speed.

Note: The joints in the crosshead and crankpin bearings have a strength that, for a short time, will accept the loads at full speed without compression in the cylinder. However, to avoid unnecessary wear and pitting at the joint faces, it is recommended that, when running a unit continuously with the compression cut-out, the engine speed is reduced to 55% of MCR speed, which is normally sufficient to maneuver the vessel.
During maneuvers, if found necessary, the engine speed can be raised to 80% of MCR speed for a short period, for example 15 minutes.
Under these circumstances, in order to ensure that the engine speed is kept within a safe upper limit, the overspeed level of the engine must be lowered to 83 % of MCR speed.

Process of Combustion Cut Out. Exhaust Valve closed. Piston still working in cylinder.

This measure may be used if, for instance, the exhaust valve or the actuating gear is defective.

The procedure is as follow:

    • Cut out the fuel pump by lifting and securing the roller guide.
    • Put the exhaust valve out of action so that the valve remains closed (lift the guide or stop the oil supply and remove the hydraulic pipe).

Please note that, the cylinder cooling water and piston cooling oil must not be cut out.

Process of piston, piston rod, and crosshead suspended in the engine. Connecting rod out

This measure may be used if, for instance, serious defects in piston, piston rod, connecting rod, cylinder cover, cylinder liner and crosshead.

The procedure is as follow:

    • Cut out the fuel pump by lifting and fixing the roller guide.
    • Put the exhaust valve out of action so that the valve remains closed.
    • Dismantle the starting air pipe. Blank off the main pipe and the control air pipe for the pertaining cylinder.
    • Suspend the piston, piston rod and crosshead, and take the connecting rod out of the  crankcase.
    • Blank off the oil inlet to the crosshead.
    • Set the cylinder lubricator for the pertaining cylinder, to ‘ ‘zero’’ delivery.

Please note that, in this case the blanking-off of the starting air supply is particularly important, as otherwise the supply of starting air will blow down the suspended engine components.

Precautions and Measures for Cutting Out a Main Engine Unit

    • Safety Protocols: The utmost priority when cutting out a main engine unit is ensuring the safety of the vessel, crew, and engineers involved. Marine engineers must follow established safety protocols, wear appropriate personal protective equipment (PPE), and coordinate with the ship’s personnel to minimize risks during the procedure.

    • Communication and Coordination: Effective communication between the marine engineer, engine room crew, and bridge team is crucial. The bridge team must be aware of any changes in engine configuration to adjust vessel operations accordingly and maintain situational awareness.

    • Monitoring and Alarms: While cutting out combustion, continuous monitoring of engine parameters, alarms, and performance indicators is essential. Any unusual readings or abnormalities should be promptly reported and addressed to prevent further complications.

    • Documentation: It is vital to maintain comprehensive documentation throughout the process, including detailed reports of the engine condition, actions taken, and any observations made during the combustion cut-out. This information assists in analyzing the cause of the malfunction and aids in future maintenance planning.

In conclusion, cutting out the combustion on a main engine unit is a critical procedure that marine engineers may need to undertake to safeguard vessel operations and prevent further damage. Whether due to engine malfunction, contamination, or maintenance requirements, this process requires careful assessment, preparation, and adherence to safety protocols. By following the necessary precautions and measures, marine engineers can effectively isolate and address the issues affecting the main engine unit, ensuring the safety, efficiency, and reliability of the vessel’s propulsion system.

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What do you need to know about “Visatron” oil mist detector

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Oil mist detectors are devices that are meant to protect large diesel engines of all applications against serious damage originating from crank-drive bearings or piston components overheating.

 

 

In case of “Visatron” oil mist detector, the atmosphere of the crankcase compartment is continuously drawn out by means of header pipes sampling system from each crankcase compartment and directed through an optical opacity measuring track.

The suction vacuum required is generated through a wear-free air jet pump in the device, fed with the compressed air (drive air), usually from engine control air system.

The sample flow, consisting of the drawn in atmosphere of the crankcase compartment, is guided through an optical channel for measuring turbidity (opacity). The sample flow is measured by absorption of infrared light.

Opacity percentage is used as the dimensional unit of the turbidity:

    • 100 % opacity means total absorption
    • 0% opacity means no absorption

Oil mist becomes explosive from a concentration of approx. 50 mg of atomized oil in 1 liter of air and up, which correspond to an opacity of approx. 40 %. To learn more about this, please follow this link.

The alarm level sensitivity for different models of “Visatron” oil mist detectors are as per below table:

These devices are very reliable and require minimum maintenance from the crew side.

However, there are some periodical performance test and calibration that are required in order to ensure that the device is working as intended and to ensure the best protection for your engine.

The performance test and calibration must be done when the engine is stopped and vessel is at anchor or safely moored in port.

You must be aware that during the performance test the engine is not monitored by the oil mist detector.

The performance test is done following the below steps (here there is an example for Visatron VN 93 model):

    • Open the control cover for the measuring head

    • Wait until the READY-LED is switched off (approx. 10 sec)

    • As above the following display appears.
    • Blind the light beam of the measuring track with a wooden vane or a similar object.

    • At devices VN 116/93 and VN 215/93 the damage check starts on the display damage compartment as can be seen in the above picture.
    • When the alarm level is reached the TEST-LED lights up (TEST-ALARM). To set back the TEST-ALARM touch the ENTER-RESET button for more than 1 second and TEST-LED goes off.
    • Close the control cover of the measuring head.
    • After approx. 15 seconds the device is back in the normal operation.

A live test with test vapour can be carried out at the engine stand still when vessel is at anchor or safely moored in port.

The test is done as follow:

    • Open the crankcase or, more convenient, disconnect one of the sampling pipes which leads to the oil mist detector.
    • By using a smoke detector test spray, spray a short burst of vapour into the pipe or inside crankcase collecting funnel.
    • Allow the oil mist detector to draw the vapours for minimum 20 seconds.
    • Depending of the vapour density and suction time, whether an oil mist alarm is triggered or an oil mist alarm is triggered and a search run starts on the display damage compartment (VN 215/93 model).

As a maintenance, the requirements are as follow:

  • Monthly maintenance: check the negative pressure in the measuring head (range 60 – 80 mm H2O).
      • The negative (suction) pressure must be calibrated by adjusting the pressure regulator when the engine is at a standstill.
      • Make sure engine room ventilation is in operation (pressure difference in engine room)
      • Pour water inside the U-tube manometer utilizing the bottle from the service box. Both tubes shall be filled equally to the half of the scale of the manometer and must be on the same level when the manometer is not connected to the oil mist detector.
      • Loosen nut (1) and turn setscrew (2) in clockwise direction slowly up to the stop.

      • Open safety cover (3) at the throttle (5) and manually turn the setscrew (4) in clockwise direction slowly up to the stop.
      • Make sure that compressed air is open (7 bar)
      • Connect the U-tube manometer to the oil mist detector quick connection as below and it should show 0 pressure.

      • Turn setscrew (4) in counterclockwise direction until the U-tube manometer indicates a negative pressure of 80 mm H2O
      • Close safety cover
      • Turn setscrew (2) in counterclockwise direction until the negative pressure is only 60 mm H2O

      • Tight counter nut (1)
      • Disconnect U-tube manometer.
  • Quarterly maintenance:
      • replace the sintered bronze filters in the measuring head. The filters must be replaced and not cleaned.

        • clean the infrared filter glasses in the measuring head. Use only cotton buds to clean these filter glasses as there is a risk of scratching those.

  • Six monthly maintenance ( only on devices equipped with optional siphon block): remove siphon block plug and blow clean with compressed air (max. 7 bar).
  • Annually maintenance: replace sintered bronze filter in the pressure reducer.

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Source and Bibliography:

  • Source and credit:  Schaller Automation