Diesel engine damage due to mis-application or mis use of generating set

Diesel engines can suffer damage as a result of mis-application or mis use – namely internal glazing and carbon buildup. This is a common problem in generator sets caused by failure to follow application and operating guidelines – ideally diesel engines should run at least around 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.

Internal glazing and carbon buildup is due to prolonged periods of running at low speeds and/or low loads. Such conditions may occur when an engine is left idling as a ‘standby’ generating unit, ready to run up when needed, (mis use); if the engine powering the set is over-powered (mis application) for the load applied to it, causing the diesel unit to be under-loaded, or as is very often the case, when sets are started and run off load as a test (mis use).

Running an engine under low loads causes low cylinder pressures and consequent poor piston ring sealing since this relies on the gas pressure to force them against the oil film on the bores to form the seal. Low cylinder pressures causes poor combustion and resultant low combustion pressures and temperatures.

This poor combustion leads to soot formation and unburnt fuel residues which clogs and gums piston rings. This causes a further drop in sealing efficiency and exacerbates the initial low pressure. Glazing occurs when hot combustion gases blow past the now poorly-sealing piston rings, causing the lubricating oil on the cylinder walls to ‘flash burn’, creating an enamel-like glaze which smooths the bore and removes the effect of the intricate pattern of honing marks machined into the bore surface. which are there to hold oil and return it to the crankcase via the scraper ring.

Hard carbon also forms from poor combustion and this is highly abrasive and scrapes the honing marks on the bores leading to bore polishing, which then leads to increased oil consumption (blue smoking) and yet further loss of pressure, since the oil film trapped in the honing marks is intended to maintain the piston seal and pressures.

Un-burnt fuel leaks past the piston rings and contaminates the lubricating oil. Poor combustion causes the injectors to become clogged with soot, causing further deterioration in combustion and black smoking.

The problem is increased further the formation of acids in the engine oil caused by condensed water and combustion by-products which would normally boil off at higher temperatures. This acidic build-up in the lubricating oil causes slow but ultimately damaging wear to bearing surfaces.

This cycle of degradation means that the engine soon becomes irreversibly damaged and may not start at all and will no longer be able to reach full power when required.

Under loaded running inevitably causes not only white smoke from unburnt fuel but over time is joined by the blue smoke of burnt lubricating oil leaking past the damaged piston rings, and the black smoke caused by the damaged injectors. This pollution is unacceptable to the authorities and any neighbours.

Once glazing or carbon build up has occurred, it can only be cured by stripping down the engine and re-boring the cylinder bores, machining new honing marks and stripping, cleaning and de-coking combustion chambers, fuel injector nozzles and valves. If detected in the early stages, running an engine at maximum load to raise the internal pressures and temperatures, allows the piston rings to scrape glaze off the bores and allow carbon buildup to be burnt off. However, if glazing has progressed to the stage where the piston rings have seized into their grooves this will not have any effect.

The situation can be prevented by carefully selecting the generator set in accordance with manufacturers printed guidelines.

For emergency only sets, which are islanded, the emergency load is often only about 1/4 of the sets standby rating, this apparent over size being necessitated to be able to meet starting loads and minimising starting voltage drop. Hence the available load is not usually enough for load testing and again engine damage will result if this us used as the weekly or monthly load test. This situation can be dealt with by hiring in a load bank for regular testing, or installing a permanent load bank. Both these options cost money in terms of engine wear and fuel use but are better than the alternative of under loading the engine. For remote locations a Salt water rheostat can be readilly constructed.

Often the best solution in these cases will be to convert the set to parallel running and feed power into the grid, if available, once a month on load test, and or enrolling the set in utility Reserve Service type schemes, thereby gaining revenue from the fuel burnt

Effects of Water on Diesel Fuel & Oil

Premature engine ware including pitting of bearings is a indication of water contamination. The water has two effects; it causes corrosion of the surfaces, and it also disrupts or degrades the mechanism of lubrication. Rolling bearing lubrication is by elastohydrodynamic action (EHL or EHD lubrication), and the presence of water tends to inhibit the formation of the EHL film. Even 0.1% of water has a significant effect, and 1% water can reduce bearing life by a factor of 10.

BioDiesel & Contamination By Water

Biodiesel may contain small but problematic quantities of water. Although it is not miscible with water, it is, like ethanol, hygroscopic (absorbs water from atmospheric moisture). One of the reasons biodiesel can absorb water is the persistence of mono and diglycerides left over from an incomplete reaction. These molecules can act as an emulsifier, allowing water to mix with the biodiesel. In addition, there may be water that is residual to processing or resulting from storage tank condensation. The presence of water is a problem because:

• Water reduces the heat of combustion of the bulk fuel. This means more smoke, harder starting, less power.
• Water causes corrosion of vital fuel system components: fuel pumps, injector pumps, fuel lines, etc.
• Water & microbes cause the paper element filters in the system to fail (rot), which in turn results in premature failure of the fuel pump due to ingestion of large particles.
• Water freezes to form ice crystals near 0C (32F). These crystals provide sites for nucleation and accelerate the gelling of the residual fuel.
• Water accelerates the growth of microbe colonies, which can plug up a fuel system. Biodiesel users who have heated fuel tanks therefore face a year-round microbe problem.
• Additionally, water can cause pitting in the pistons on a diesel engine.

Before you start troubleshooting.

Safety is the primary concern in troubleshooting generators. If you are not sure of what your doing ask or leave it to a professional. Understand what you are doing and use caution. There is a risk of injury from moving parts, heat and live electrical wires that can shock and kill you.

The first step in generator troubleshooting is to conduct a visual inspection before doing any electrical tests. Looking the generator over carefully should expose any environmental factors that might contribute to the problem. As you remove the generator cover and begin your inspection, look for the following:

• Rusted or corroded connections. An oxidized connection will prevent the circuit from being completed. This applies not only to the major cables externally, but also to the electronic control devices internally.
• Signs of overheating. Discoloration and or burnt smells. Windings that are normally copper in color that may have turned black. The insulating sprays that manufacturers use to insulate the windings may vary in color from shades of reddish brown to light brown to dark brown, so try to compare the color to that of a new unit.
• Wire insulation that is heat-hardened. Fabric and plastic insulation hardens over time due to heat exposure and overheating. Long-term heating should be more uniform. A short, excessive heat cycle may have less hardening and burning at the unit’s outer perimeters and excessive heat signs toward the center or heat source.
• Insects that have developed a community inside the generator. Their nests and debris can cause electrical shorts. Generators left out in the elements, such as for running water wells, provide a nice home for critters such as spiders, wasps, and mice.
• Loose bolts, screws, and fasteners. This condition will either prevent full-time service or give intermittent service depending on the situation.

Engine Will Not Start

A diesel mechanic will often find a failure in a diesel engine to be a direct result of something the user did or failed to do rather then a manufacturing defect or product quality. Warranties only cover manufacturing defects and not failure due to neglect or abuse. Trying to fix a problem yourself is often the best first step. To do the work yourself you need to understand some basic stuff that we will cover here.

When a diesel engine stops running or fails to start, the most common cause is a fuel problem. Checking the fuel system is your first step.

Your diesel generator is designed to work with normal automotive diesel fuel. Using anything else will leave evidence it behind. In warranty claims manufactures and dealers have tests to check for traces of wrong fuel used and look for deposits in the combustion chamber and fuel system to void a warranty. If you use the fuel it was designed to use then this will never be an issue.

Here is how the fuel system works. Fuel from the tank flows by gravity through a fuel filter. The filter may be inside the tank or mounted outside. The fuel filter housing often has a turn off valve on it. Next the fuel goes to the pump where it is pumped under very high pressure to the fuel injector. The amount of fuel pumped is controlled by the throttle position, the connection is internal and it adjusts the fuel pump volume. This effects the engine speed. The throttle position is also fine tuned by a engine speed governor to control the engine speed. Many fuel pumps now have a electric valve on them to also turn off the fuel and cause the engine to shut down if needed. Some will just release the throttle to do the same thing.

How to check the fuel system

Make sure you are using ONLY normal automotive diesel fuel you purchase from a gas station. Do not use furnace oil, red dye fuel or anything else. In the winter time fuel that is very cold will gell. Fuel that gells will break apart and will also clog filters and fuel lines.

Check fuel shut off valves under the fuel tank and on the inline fuel filter. If you are not sure if they are open then remove the rubber fuel line from the fuel pump and see if fuel flows out feely.

Anytime you run out of fuel it will cause air to reach the fuel pump and stall the engine. Even if you refill the tank air is still trapped in there and the pump will not work. Often it can not pass air because the air will compress where the fuel does not and it passes just fine. Trying to pass air through the pump will damage it and may also damage the fuel injector. You must remove the air by removing the rubber fuel line off the fuel pump and let the fuel run out until all air is removed. Do not crank the engine trying to remove the air or you will damage the fuel pump and or the fuel injector.

Air in the fuel can also be a cause of hard starting or a no start condition. Air can make the engine die after it starts, and make restarting difficult. Air can enter the system through any break in the fuel line or via a bleedback condition.

The best way to check if the fuel pump is working is to remove the fuel injector and with the fuel line connected and snug, fuel should spray out in 4 directions when cranking. (It is under high pressure, keep eyes protected and fingers away from the tip) Before you do it, make sure the throttle is in the run position. Check for any springs that may have come off the throttle assembly while your at it. You can also bleed any remaining air out by lessening the high pressure fuel line at the injector and cracking then replace it once there is a steady trickle of fuel coming out when you crank the engine.

Some fuel problems are a result of the electric fuel valve and that it has failed. It can get stuck from deposits in the fuel or even a grain of sand. The fuel valve can easily be removed and cleaned to fix the problem. When it fails to open fuel does not get into the fuel pump. Remove it, take out the plunger and spring and replace it. See if the fuel pump works again and you can start your generator.

The electric fuel valve is used to turn off the fuel supply and stop the engine if there is low oil pressue, you turn off the key switch or press off on the remote control. If it does not work and you disabled it then the only way to turn off the engine will be to release the throttle and or close some other fuel valve.

Compression is the second thing that is required for a diesel engine to work. Diesel motors work by compressing air so much and so fast that it creates a lot of heat. Enough heat and it will ignite the air and fuel mixture.

When cranking the engine and trying to start up it is important for the engine turns fast enough for enough compression to happen. Too slow cranking will not create enough heat to start the engine. Make sure your battery is fully charged and all connections are snug. If you can move any battery cable or wiring up to the starter then the connections are poor and it will result in slower cranking.

If you are at an altitude over 3000 feet then you will also have problems starting your engine. The air is too thin and there is not enough to compress and cause all the heat necessary for the engine to work. If you manage to get it started, you will not have complete combustion, black smoke will be visible because there is not enough heat to burn all the fuel completely. Further engine damage will occur.

Portable diesel engines use mechanical valve lifters and in the beginning they settle into place and ware down the most. You need to adjust the play between the rocker arm and the valve. If you do not then rather then it pushing the air intake and exhaust valves open they work like hammers and will quickly fail or there will be enough play that they will fall off. Checking it is easy. Remove the rocker cover and inspect it as shown below. Adjust it if necessary and look to see if the adjustment screw is broken off. This may happen if it was working like a hammer rather then pushing the valves as it should.

Fuel Delivery & Fuel Injectors

Fuel injectors require a high quality finely filtered diesel fuel to work.

Diesel injectors can suffer from the same kinds of ailments as gasoline injectors, including varnish deposits, clogging, wear and leakage. Today’s low sulfur diesel fuels are MORE likely to leave varnish and gum deposits on injectors, and also provide less lubrication so using a good fuel additive will help to keep things flowing smoothly.

When your fuel injectors get dirty or start leaking the result is often back smoke. You will notice a rough engine speed too. The dirty fuel injector can not create the fine spray needed to properly mix with the air and will not burn correctly as a result. But it is not always the problem. Black smoke is usually a signal that there’s too much fuel. Not having enough air will also cause this. Check that your air filter is not clogged and before changing your fuel injector check the valves. They should be adjusted first. When they are out of adjustment is will also result in not enough air exchange and incomplete combustion.

Here is how they work. Fuel is supplied from the fuel tank and is passed through a fuel filter system. This is the engines first and only line of defense, and it is the filters task to remove any sludge, sediment, rust or other contaminants that have found their way into the fuel tank. These types of systems are commonly fitted with 20-micron filters manufactured from tightly woven cellulose material. This filter is designed to mechanically prevent any abrasive material from entering the sensitive fuel injection system. A filter can only filter a set amount of sediment before blocking and becoming useless. Since most generators transfer fuel from the tank to the fuel pump by grafity, it does not take much to stop the normal flow of fuel.

Next a single feed then directs the diesel fuel into a high-pressure fuel pump. Here the fuel is pressurized and sent to the fuel injector nozzle in the engine cylinder. The pump is a plunger that is activated by a bump or lobe on the cam shaft that makes contact with it.

The amount of fuel the pump will pump is controlled by a metering valve. The amount of fuel changes the engine speed. The valve is part of the fuel pump. What you can see is the lever on the fuel pump as it moves to open and close the pump fuel flow. It looks like a arm with a pin on it. It fits into what looks like a fork arm that is connected to the throttle. One must fit inside the other for the throttle and governor to control the pump. If you take off the governor lever inspection cover then you can see it. You can move the throttle and see it move a lever on the fuel pump. If it is out of place then the engine speed will be erratic. It may have jumped out of place of you removed the fuel pump or have at any time forced put force on the throttle. It is a simple check to see see if it working correctly.

Back to the fuel pump pumping….. It is at this point that fuel quality plays a vital role. Diesel floods this mechanical device and all lubrication inside the fuel pump is now provided by the lubricating properties of the diesel fuel. Sediment in the fuel can act as a grinding paste, sulfur can mix with the water to form a mild sulfuric acid and cause chemical etching, water can cause rust and if the base fuel does not have enough lubricity some parts will simply cease. All this can cause catastrophic failure in the pump.

This pressurized fuel arrives at the injector nozzle. At a set pressure the needle within the injector will open and it will spray a set amount of diesel into the chamber. There are tiny holes at the tip of each injector nozzle that are designed to give an even spread of diesel fuel before it ignites.

Again the fuel quality is of utmost importance. If the viscosity of the diesel is perhaps to thick or to thin then the spray pattern will not be correct and the fuel will not atomize and achieve the correct combustion. Incomplete combustion can cause excessive exhaust smoke and carbon build up in the chamber and around the injector nozzle tips which could further alter the spray pattern or even block the tiny holes at the end of the injectors.