|Compositions of Diesel Engine Cooling System|
[It's relates to supplemental coolant additives, particularly for
The heavy duty diesel engines impose unique and stringent requirements on the cooling system; and the expected life to overhaul for a heavy duty diesel engine is generally four to five times that of an automobile engine, despite the fact that the load factor is usually over twice as much and the gross vehicle weight per horsepower is usually five to eight times as high. For a diesel to perform in this manner, good cooling system maintenance is necessary.
Heavy load factor for a heavy duty diesel engine means that cooling system efficiency is very important. Waste heat must flow freely through cylinder liners, head, oil cooler, aftercooler and radiator. If this process of heat transfer is interrupted, wear rates go up and engine efficiency goes down. For instance, the scaling or fouling of cylinder liners can result in greatly increased ring wear and substantially reduce the engine operating life between overhauls. Complicating this is the fact that diesel engine coolants often contain a higher level of contaminants, such as precipitated additives, dirt and oil.
A heavy duty diesel engine is often built with replaceable or wet cylinder liners. This makes the engine more easily rebuildable but also makes cooling system maintenance critical. Because of liner vibration due to piston slap, small holes or pits can develop and perforate the liner in only 30,000 miles of operation if only tap water is used in the cooling system.
On the other hand, if an adequate amount of a properly formulated supplemental coolant additive is periodically added to the coolant, the liners can last 500,000 miles or more with little or no pitting damage. For this reason, heavy duty supplemental coolant additives must not compromise in this area of performance. Also, diesel cooling systems may employ cast iron or steel water pump impellers, which are susceptible to cavitation corrosion.
For the unique demands placed on cooling systems for heavy duty diesel engines, supplemental coolant additives have assumed an important role for the long term protection of their cooling systems. At the present time, substantially all of the heavy duty diesel engine manufacturers in the United States recommend the use of some type of supplemental coolant additive.
Antifreeze compositions, historically, have been formulated to meet the coolant needs of automobiles but have not satisfactorily met the needs of a diesel engine. Accordingly, supplemental coolant additives are added to the diesel engine cooling system initially to make up for the deficiencies of the antifreeze solutions customarily used. Supplemental coolant additives are also added to the cooling system at each oil change to replace additives lost due to dilution and additive depletion.
Low temperature performance is very important for a heavy duty diesel engine. Coolant temperatures can drop to 80° F. if a diesel is idled or involved in stop and go service at low loads in cold weather. The supplemental coolant additives should not foam excessively at higher temperatures of say 190° F. or at ambient temperatures. Under field conditions, the defoamer used in a supplemental coolant additive must be thermally stable and excessive amounts cannot be lost to metal surfaces if it is to perform adequately.
Heavy duty antifreeze can be formulated to provide short term liner pitting protection, but it will not provide long term protection under the conditions of heavy duty diesel engine use. It has been stated that conventional antifreezes have a service life of approximately 15,000 miles. For automotive service, this mileage may take about one year to accumulate, but in some line haul diesel engine truck fleet operations, 15,000 miles is accumulated in one month. To maintain an adequate level of additive in the system, the heavy duty antifreeze could be changed on a monthly basis, but this is costly. It is much more cost effective to use a supplemental coolant additive and not replace the antifreeze until 180,000 miles.
A supplemental coolant additive should prevent scaling of heat transfer surfaces. Scaling is usually used to refer to inorganic deposits that are composed of minerals from make-up water, precipitated corrosion inhibitors and corrosion products. Filtration, ion exchange resin, water soluble polymers, or chelating agents have been used to deal with the scaling problem. The more effective approach is to use a combination of the above.
On the other hand, fouling is generally used to denote deposits of an organic/biological nature. Fouling in a heavy duty cooling system usually involves lubricating oil contamination but rarely biological growth. Lubricating oil fouling is quite common in heavy duty systems. One random survey of over 200 trucks showed over 20 percent with various amounts of lube oil in the cooling system. A properly designed supplemental cooling additive must have a degree of detergency to prevent oil and other organic contaminants from fouling heat transfer surfaces and causing corrosion.
Compatibility problems can arise because a component of the antifreeze solution chemically reacts with a component of the supplemental coolant additive. For example, when chromate based supplemental coolant additives were added to antifreeze which contained arsenite, the two additives reacted immediately, neutralizing each other and forming large amounts of chromic hydroxide precipitant. The end result was a plugged cooling system and corrosion problems.
Compatibility problems can also occur because the limit of solubility of a component has been exceeded. as for example, if a silicate containing supplemental coolant additive is added to an antifreeze which contains large amounts of silicate, the solubility of silicate in the solution may be exceeded and silicate gelation takes place. The cooling system can tolerate a moderate amount of gelation but heavy gelation will plug the cooling system filter and then plug cab heater cores and radiators.
The formation of disodium phosphate (Na2HPO4) crystals at low temperature is another antifreeze compatibility. Since commercial antifreezes contain varying amounts of sodium and phosphate, the sodium or phosphate levels in the supplemental coolant additive must be low enough to keep the levels in the coolant mixture within the solubility limit.
In a typical on highway heavy duty diesel engine cooling system, flow rate can range from 80 to 150 gallons per minute. This means that flow velocities can reach 8 to 10 feet per second. Tests have shown that solder and aluminum are sensitive to the effects of high flow rate.
Some water used in the cooling system can be very hard or corrosive. Conventional supplemental coolant additives and antifreezes have not provided good aluminum protection in all cases. Silicate levels have been increased by many antifreeze suppliers to resolve the problem in cars. However, when these high silicate antifreezes are used with conventional supplemental coolant additives, silicate gelation can occur. Aluminum protection can be provided without resorting to increased silicate levels by using other ingredients to provide protection even with the silicate level being reduced.
Borate-nitrite supplemental coolant additives have been the predominant type used in the United States and many other areas of the world (during the time period of 1970-1985). This type of additive is usually formulated with relatively high levels of nitrite and silicate. Nitrite, typically used to prevent liner pitting, is somewhat aggressive toward solder. If the nitrite level is reduced by replacing all or part of it with a different ingredient which is not aggressive toward lead yet still provides liner pitting protection, lead corrosion can be reduced.
Fluorescent dyes used as external coolant leak detectors many years ago. Internal coolant leakage into the lubricant has been difficult to detect. Therefore, a trace element in the coolant is useful for detecting coolant leakage into the lub oil during routine oil anaylsis. The element should not normally be present in lube oil as additives nor as wear metals. It should not be toxic, expensive or detrimental to performance of the coolant.
Conventional supplemental coolant additives have typically provided ingredients for liner pitting protection, scale inhibition, buffering, defoaming and general corrosion protection. Sometimes ingredients for external leakage detection have also been provided. These supplemental coolant additives have been added to the coolant in the form of liquid,
It is provided that the novel supplemental coolant additive compositions can be used in the cooling systems for diesel engines to improve the performance and extend the operating life thereof plus reduce maintenance costs associated with diesel engine cooling systems. And the compositions not only having the normal performance of conventional supplemental coolant additives, but also provide improved solder and aluminum protection plus better antifreeze compatibility. It is a further object of this invention to provide compositions which offer two additional attributes not offered by conventional supplemental coolant additives, a surfactant/detergent to reduce fouling and a trace element to allow detection of coolant leakage into the lube oil.
Then it is provided that, a heavy duty supplemental cooling additive composition containing a combination of components which coact to provide improved aluminum protection in hard water, improved lead solder protection and improved antifreeze compatibility. These improvements are achieved without sacrificing liner pitting protection and while minimizing silicate gelation and low temperature crystallization of disodium phosphate.
The novel heavy duty supplemental cooling additive of this invention comprises a buffer, a cavitation liner pitting inhibitor, a metal corrosion and hot surface corrosion inhibitor, a defoamer, a hot surface deposition and scale inhibitor and a detergent to reduce fouling problems. The buffer component is employed to maintain a substantially neutral pH in
Additionally the potassium serves as a trace element whereby leakage of the coolant into lubricating oil can readily be detected. The presence of potassium in the lubricating oil can be readily detected by known procedures.
Unlike prior art compositions, the heavy duty supplemental cooling composition of this invention also includes a surfactant or detergent which reduces fouling of heat transfer surfaces in the cooling system by lubricating oil or other organic contaminants.
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