Posts

How does a heat exchanger work?

 

Your engine’s cooling system is highly critical; the combustion process produces an enormous amount of heat, and that heat must be removed or dissipated. If heat is not removed, cylinder and engine block damage may quickly result.

Heat exchangers cool the engine, but work a little differently and more efficiently than a simple raw water cooling system. A heat exchanger consists of a series of tubes, or coils, that fluid flows through. This fluid is enclosed (either cooland or distilled water). Additionally, marine heat exchangers are encased by a jacket, through which raw water (fresh water or sea water) flows through, cooling the enclosed fluid, removing the heat, and exiting the system through the exhaust. The minerals in sea water mean that scaling, or build up, can occur, which is why heat exchangers usually require periodic maintenance. Mineral build up drastically reduces the efficiency of the heat exchanger and thus, the cooling capacity.

This is also why a blocked strainer or faulty impeller quickly damages an engine. When blocked by debris (especially plastic bags), without the raw water to cool the enclosed system, the engine quickly overheats, sometimes in a matter of mere seconds.

 

Best of 2014 – Engine Room Ventilation

 

 

We wish all MarineDiesel customers a happy holiday season. Our factory will close from December 22 through January 5. For the balance of the year, we will be re-running our most popular articles from 2014, based on the number of visitors. We will start new daily articles in the New Year. We hope that you continue to find them interesting.

MarineDiesel designs its’engines with reliability and service life being key concerns. Using a Duramax block as a foundation for our VGT Series of engines, the product is reliable and trouble-free as long as regular maintenance is performed when due.

There are, however, two situations that can greatly reduce engine life. The first is the use of dirty fuel. The second is inadequate ventilation of the engine compartment.

This situation is most prevalent in tropical, or hot, climates.

All engines produce a tremendous amount of heat. That is how they operate and why they produce power. In order to operate continuously, they must be adequately cooled, with ample ventilation provided for continued operation.

This is where problems can arise. The VGT Series, in particular, being so compact, is often used in very small craft, such as RHIBs, that have very small engine compartments as part of their design. Small, tight, engine compartments tend to lack much ventilation, and therefore ventilation must be provided in order to ensure trouble free operation.

From MDS, our service team:

Engine power is affected by a number of different external factors. Among the most important are air pressure and volume, air temperature and exhaust backpressure. Deviations from the normal values affect engine performance, function and reliability.
Diesel engines require a large amount of air compared to petrol engines. Reductions from the required values show up first of all as an increase in exhaust black smoke. This can be particularly noticeable at the planing threshold when the engine torque demands are high. If the deviations from the required values are great, the engine will lose power. This power loss can
be so great that a planing boat cannot pass through the planing threshold. For the engine to function properly and give full power, it is absolutely essential that both the inlet and outlet air ducts are sufficiently dimensioned and installed correctly.

Two main conditions must be fulfilled.

1. The engine must get enough air (oxygen) to allow efficient combustion.
2. The engine room must be ventilated so that the temperature can be kept down to an acceptable level.

Ventilation is also important to keep the engine’s electrical equipment and fuel system temperature at an acceptable level and for general cooling of engine components.

Basic design.

Engine space ventilation should be considered at an early stage and well before the engine is installed as it is often has to be integrated into the boat structure. Guidelines for air intake area are provided in the installation data and we have provided basic formulae in this section if you wish to calculate your own. Air intake area should never be underspecified, it is always better to have too much than too little. Intake air should always be directed to the bottom of the space and exhausted at the highest part preferably on the opposite diagonal to promote good circulation and natural convection.

There are two schools of thought concerning engine space ventilation, that of the engine manufacturer and that of the boat builder. Most engine manufacturers recommend forcing air into the engine space to provide positive pressure to ensure adequate air supply and ventilation for the engine. Boat builders on the other hand tend to favour extracting air from the engine space to provide a small negative pressure, this can prevent engine odours and fumes entering the passenger compartment through cable and hose ducting, etc.
Either system can be used for MarineDiesel engines but we prefer forcing air into the engine space and having properly sealed engine rooms to prevent odours and fumes. If air is to be drawn out using a fan then we recommend adding the CFM of the fan to that of the engine when working out your air intake area.

Engine room depression.

The maximum engine room depression is 0.5 kPa at full speed, this should be checked in every circumstance irrespective of the type ventilation system used.

Dimension of air intakes and ducts.

The engine itself sucks in air very effectively and naturally will take in air from any direction. Should the inlet or outlet air ducts be under dimensioned, the engine will consequently suck air from both ducts and no ventilation air will go out through the outlet air ducts. This causes dangerously high engine room temperatures and potential engine damage. Most of the radiant heat from the engine must be transported out of the engine room. This is an absolute requirement to keep the engine room temperature below the permitted maximum limit.

Engine room temperature.

Remembering that the engine’s performance figures apply at a test temperature of +25°C, it is important that the inlet air temperature is kept as low as possible. The temperature of the inlet air at the air filters should not be higher than +25 °C for full power output.

There is always a loss of power with increased temperatures and if the engine’s inlet air is constantly above +45°C the engine ECM will de-rate the engine as a safety measure. During sea trials the air temperature in the air filter should not exceed 20 °C above ambient temperature or 45°C maximum.

Location of air ducts.

Air intakes should be located where there is a clean flow of air and away from low pressure zones of the boat structure. They should be designed in such a way as not to allow water ingress into the engine space and provide a dry air supply for the engine(s). Care should be exercised with multiple engine installations to ensure air is delivered effectively to all the engines. If louvers are used, the air inlets should be louvered forward and the air outlets louvered towards the stern, this will encourage ventilation on naturally vented systems. Blowers and/or extractors can also be incorporated if deemed necessary. The channels or ducts for the engine air supply should be routed up as close as possible to the air filters but with a minimum distance of 20–30 cm (8–12″) as a precaution should water enter them.

All channels and ducts must be routed so that the least possible flow resistance is obtained. The bends must not be sharp but softly rounded. The smallest radius should be equal to the internal area. Restrictions must always be avoided.
The ducts should be cut obliquely at the ends to assist flow.

NOTE!

Air intakes or outlet holes must never be installed in the transom. The air in this area is turbulent and usually a mix of water and exhaust fumes and must therefore never be allowed to enter the engine or boat.

Function of air intakes.

Air intakes and outlets must function well even in bad weather and must therefore have efficient water traps. Soundproofing must usually be built in. The air intake and outlet should be placed as far away from each other as possible so that a good
through-flow is obtained. If the intake and outlet are too close, the air can re circulate resulting in poor ventilation.

Engine’s air consumption.

The engine consumes a certain amount of air in the combustion process. This requires a minimum internal area of air supply ducting, the minimum area can be calculated by using this formula.

A = 1.9 × engine power output in Kw
A = Area in cm²

The area of the outlet ventilation ducting can be calculated to be a minimum of a third of the air intake ducting area. The value applies for non-restricted intake and up to 1m (3.3 ft) duct length with only one 90 degree bend. The bending radius should be at least twice the internal area. If longer ducts or more bends are used, the area is corrected by multiplying a coefficient from Table
1 below.

eng vent1

Ambient temperature.

The ambient air temperature, (outdoor air temperature) is assumed to be +30°C (86°F). Correction factors as per Table 2 below should be applied as required by multiplying the calculated area by the correction factor.

eng vent2

A - Air should exit the engine bay and the upper section B – Air should enter the engine bay at the lower section

A – Air should exit the engine bay and the upper section
B – Air should enter the engine bay at the lower section

 

 

 

How to keep heat from ruining your marine engine

 

 

All engines produce heat; A lot of it. This heat, if not dissipated, will quickly ruin your engine, necessitating expensive and time-consuming repairs. In fact, heat-related problems are a common maintenance issue, not only with MarineDiesel engines, but engines from all manufacturers.

How do you control heat?

Well, the first step is at the manufacturer’s end of things. MarineDiesel designed its’ engines with specific cooling systems for the application. The engines were tested in a lab, and in the field, before they were released for sale into the market. In fact, most changes to our engine product line over the years have been related to increases in the heat removal efficiency of our cooling systems. This is not as easy as it might sound. Emissions regulations, weight, power output, and engine size all are impacted by these changes.

If the engine will be used in a tropical environment, the challenges are multiplied significantly. As a general rule, our service department sees more issues in these regions than in cooler climates in the world. This is especially important in small craft with engine compartments, rather than an engine room.

As an engine end-user, the following tips will help you keep your engine cool and running worry-free:

  1. Make absolutely certain that there is cross-ventilation in the engine compartment (See picture below). Louvers and ventilation must be designed properly, and never be blocked.
  2. Always check exhaust temperature. Catching problems when they occur is easier, and cheaper in the long term.
  3. Install a blower in the engine compartment, if necessary.
  4. Always maintain your grid cooler, keeping it clean and replacing it if corroded.
  5. Ditto, the heat exchanger.
  6. Always ensure that the water intakes are not blocked.

eng vent3

 

 

 

 

What is Marinization?

 

 

What is marinization?

A diesel is a diesel, right? It should work just fine whether you use it in a boat or a car.

This question occasionally comes up in inquiries to our parts department.

In theory, at least, any diesel engine should operate on any vehicle, land or sea. However, in the years we have been in the marine business, we have never seen one of these independent project come to a successful fruition. The normal scenario is that someone is either given, or has picked up very cheap, an old diesel automobile or truck engine, and they come to us when they cannot get it working.

Marinization is the engineering and manufacturing of engines specifically for marine use.

What are the differences between marine and land engines? There are many. However, the following systems are nearly always different: Cooling, exhaust, and gearbox.

Marine engines need to be liquid cooled. That means that they use a heat exchanger instead of a radiator. As has been written many times before on this blog, heat is an engine’s worst enemy, and the heat produced by combustion must be dispersed effectively in some manner.

As to exhaust, engines used on land typically use a dry exhaust system. Try this on the water and you will have a very noisy engine, indeed. A big issue with wet exhaust systems is that they typically require modified cylinder heads in order to function properly. That old school bus engine most certainly would require new cylinder heads.

Transmissions, or gearboxes, are another issue. We refer back to the old school bus engine. Though you might save a little on the engine, you will need a marine gearbox with proper ratio in order to use that engine on the water. Gear ratios for marine engines are substantially different than on land.

Electronics and electrical systems are also substantially different on marine engines. Something often overlooked is the need for a new control panel, since all of the gauges will be different. Wiring suitable to the marine environment is also necessary. Add in the fact that if the engine to be marinized is electronic, the ECU programming will be completely different. This problem can become extremely expensive to correct, and normally cannot be done by the average person or mechanic.

This brings us to the environment, in general. Marinized engines use components that are manufactured from non-corrosive metals and alloys. Engines used on land are not.

When all of the above is added up in the decision making process, that bargain engine most likely will not turn out to be as big of a bargain as it may seem. In our experience, nearly every one of these projects has resulted in very expensive failures.

Marinediesel has spent the money in properly engineering the marinization of our engines. We have already made the mistakes. We have engineered a bonafide marine engine, suitable for use on boats.

That is the definition of marinization and a very brief explanation about the steps necessary to accomplish the goal of diesel use on water.

 

 

 

Maintenance Tip of the Week – Strainers 10/13/2014

Maintenance Tip of the Week:

Cooling your engine adequately is one of the most critical things that needs to occur in order to ensure a long service life of your engine. Indeed, at MarineDiesel, one of the most common service issues that arises is the blockage of strainers. You could make cleaning strainers easier by installing strainers that are of a type that are easily accessible or require no tools to change. Bronze is the preferred material since it is resistant to corrosion. Always make certain that strainers are properly seated and do not leak.

Additionally, sometimes modifications of the intakes can help reduce the amount of debris that accumulates in the intake.

 

Tight spaces and tighter places

 

 

MarineDiesel engines are the lightest, and most compact, of any engine on the market in our class. That is indisputable fact.

Why does this matter?

Quite simply, MarineDiesel engines can fit into tight places that simply do not have the space for our larger competitors. On boats, especially RHIBs or small high speed craft, this is a very important product feature. RHIBs, in particular often have tiny engine compartments located immediately under the deck, with little excess room. The vessel pictured above is a recreational vessel with three engines. Engines made by our competitors would not only never fit in the limited space, but their extra weight would shift the LCG of the vessel considerably.

With catamarans or trimarans, a different problem emerges. The beam on each hull. Port or starbord, engine compartments are narrow, with little extra room.

This can be an issue in industrial applications, too. Our MDPT subsidiary is currently involved in a re-powering project involving armored vehicles. These vehicles are designed with precisely zero excess space, and the smaller, lighter MDPT engines make a big difference in vehicle performance and ease of operation.

In fact, the biggest problem we face in these cramped quarters is providing adequate cooling for the engines, whether on land or at sea. Engines produce a lot of heat, and that heat must be dissipated. Through years of experience, MarineDiesel has learned practices and techniques that provide adequate cooling, such as louver design, blowers, and engine placement.

To illustrate, see the ventilation diagram below:

A - Air should exit the engine bay and the upper section B – Air should enter the engine bay at the lower section

A – Air should exit the engine bay and the upper section
B – Air should enter the engine bay at the lower section

 

 

 

 

10 quickest ways to ruin your diesel engine

 

 

MarineDiesel prides itself on manufacturing engines of the highest quality, yet, sometimes we see things that make us scratch our heads and say, “What were they thinking?”

So, without further adieu, below is the list of ten things that we guarantee will kill your diesel engine as fast as a stick of dynamite:

  1. Not changing fuel filters, or, even worse, running without filters. (“But hey! Filters get EXPENSIVE”. Seriously, have you SEEN the fuel in Nigeria?)
  2. Not following engine break-in procedure
  3. Not changing air filters
  4. Not changing oil filters
  5. Not letting the engine warm up
  6. Not checking for leaks (at least until there is no oil left)
  7. Full throttle, 100% of the time
  8. Not starting the engine regularly. Sludge is never a good thing. (see below)
  9. Not checking fuel quality (Condensation? Nah… Not on this boat)
  10. Not checking temperatures. (You think that plastic bag blocking the strainer might cause overheating?)

BONUS: If you think that duct tape makes a permanent repair, no further comment is necessary.

sludge

Maintenance Tip of the Week – Heat Exchanger 04/07/2014

 

Maintenance tip of the Week

04/07/2014

Heat exchanger maintenance is a complex task, normally best performed by MarineDiesel factory trained dealers and distributors. This maintenance should not be ignored, as the internal parts of the heat exchanger can corrode over time, in addition to the fact that they are often stepped on and damaged in cramped engine compartments.

Maintenance Tip of the Week – Strainers 03/17/2014

 

Maintenance Tip of the Week

03/17/2014

Diesel engines produce tremendous amounts of heat energy, and that heat must be dispersed. Clogged strainers can ruin your engine quicker than just about any other cause. Always check your strainers for fouling and blockage.

Engine Room Ventilation

 

 

MarineDiesel designs its’engines with reliability and service life being key concerns. Using a Duramax block as a foundation for our VGT Series of engines, the product is reliable and trouble-free as long as regular maintenance is performed when due.

There are, however, two situations that can greatly reduce engine life. The first is the use of dirty fuel. The second is inadequate ventilation of the engine compartment.

This situation is most prevalent in tropical, or hot, climates.

All engines produce a tremendous amount of heat. That is how they operate and why they produce power. In order to operate continuously, they must be adequately cooled, with ample ventilation provided for continued operation.

This is where problems can arise. The VGT Series, in particular, being so compact, is often used in very small craft, such as RHIBs, that have very small engine compartments as part of their design. Small, tight, engine compartments tend to lack much ventilation, and therefore ventilation must be provided in order to ensure trouble free operation.

From MDS, our service team:

Engine power is affected by a number of different external factors. Among the most important are air pressure and volume, air temperature and exhaust backpressure. Deviations from the normal values affect engine performance, function and reliability.
Diesel engines require a large amount of air compared to petrol engines. Reductions from the required values show up first of all as an increase in exhaust black smoke. This can be particularly noticeable at the planing threshold when the engine torque demands are high. If the deviations from the required values are great, the engine will lose power. This power loss can
be so great that a planing boat cannot pass through the planing threshold. For the engine to function properly and give full power, it is absolutely essential that both the inlet and outlet air ducts are sufficiently dimensioned and installed correctly.

Two main conditions must be fulfilled.

1. The engine must get enough air (oxygen) to allow efficient combustion.
2. The engine room must be ventilated so that the temperature can be kept down to an acceptable level.

Ventilation is also important to keep the engine’s electrical equipment and fuel system temperature at an acceptable level and for general cooling of engine components.

Basic design.

Engine space ventilation should be considered at an early stage and well before the engine is installed as it is often has to be integrated into the boat structure. Guidelines for air intake area are provided in the installation data and we have provided basic formulae in this section if you wish to calculate your own. Air intake area should never be underspecified, it is always better to have too much than too little. Intake air should always be directed to the bottom of the space and exhausted at the highest part preferably on the opposite diagonal to promote good circulation and natural convection.

There are two schools of thought concerning engine space ventilation, that of the engine manufacturer and that of the boat builder. Most engine manufacturers recommend forcing air into the engine space to provide positive pressure to ensure adequate air supply and ventilation for the engine. Boat builders on the other hand tend to favour extracting air from the engine space to provide a small negative pressure, this can prevent engine odours and fumes entering the passenger compartment through cable and hose ducting, etc.
Either system can be used for MarineDiesel engines but we prefer forcing air into the engine space and having properly sealed engine rooms to prevent odours and fumes. If air is to be drawn out using a fan then we recommend adding the CFM of the fan to that of the engine when working out your air intake area.

Engine room depression.

The maximum engine room depression is 0.5 kPa at full speed, this should be checked in every circumstance irrespective of the type ventilation system used.

Dimension of air intakes and ducts.

The engine itself sucks in air very effectively and naturally will take in air from any direction. Should the inlet or outlet air ducts be under dimensioned, the engine will consequently suck air from both ducts and no ventilation air will go out through the outlet air ducts. This causes dangerously high engine room temperatures and potential engine damage. Most of the radiant heat from the engine must be transported out of the engine room. This is an absolute requirement to keep the engine room temperature below the permitted maximum limit.

Engine room temperature.

Remembering that the engine’s performance figures apply at a test temperature of +25°C, it is important that the inlet air temperature is kept as low as possible. The temperature of the inlet air at the air filters should not be higher than +25 °C for full power output.

There is always a loss of power with increased temperatures and if the engine’s inlet air is constantly above +45°C the engine ECM will de-rate the engine as a safety measure. During sea trials the air temperature in the air filter should not exceed 20 °C above ambient temperature or 45°C maximum.

Location of air ducts.

Air intakes should be located where there is a clean flow of air and away from low pressure zones of the boat structure. They should be designed in such a way as not to allow water ingress into the engine space and provide a dry air supply for the engine(s). Care should be exercised with multiple engine installations to ensure air is delivered effectively to all the engines. If louvers are used, the air inlets should be louvered forward and the air outlets louvered towards the stern, this will encourage ventilation on naturally vented systems. Blowers and/or extractors can also be incorporated if deemed necessary. The channels or ducts for the engine air supply should be routed up as close as possible to the air filters but with a minimum distance of 20–30 cm (8–12″) as a precaution should water enter them.

All channels and ducts must be routed so that the least possible flow resistance is obtained. The bends must not be sharp but softly rounded. The smallest radius should be equal to the internal area. Restrictions must always be avoided.
The ducts should be cut obliquely at the ends to assist flow.

NOTE!

Air intakes or outlet holes must never be installed in the transom. The air in this area is turbulent and usually a mix of water and exhaust fumes and must therefore never be allowed to enter the engine or boat.

Function of air intakes.

Air intakes and outlets must function well even in bad weather and must therefore have efficient water traps. Soundproofing must usually be built in. The air intake and outlet should be placed as far away from each other as possible so that a good
through-flow is obtained. If the intake and outlet are too close, the air can re circulate resulting in poor ventilation.

Engine’s air consumption.

The engine consumes a certain amount of air in the combustion process. This requires a minimum internal area of air supply ducting, the minimum area can be calculated by using this formula.

A = 1.9 × engine power output in Kw
A = Area in cm²

The area of the outlet ventilation ducting can be calculated to be a minimum of a third of the air intake ducting area. The value applies for non-restricted intake and up to 1m (3.3 ft) duct length with only one 90 degree bend. The bending radius should be at least twice the internal area. If longer ducts or more bends are used, the area is corrected by multiplying a coefficient from Table
1 below.

eng vent1

Ambient temperature.

The ambient air temperature, (outdoor air temperature) is assumed to be +30°C (86°F). Correction factors as per Table 2 below should be applied as required by multiplying the calculated area by the correction factor.

eng vent2

 

A - Air should exit the engine bay and the upper section B – Air should enter the engine bay at the lower section

A – Air should exit the engine bay and the upper section
B – Air should enter the engine bay at the lower section