Gasoline, diesel, CNG, LNG, LPG powered engines all produce heat. As early as 1933, university studies showed flame temperatures in an internal combustion engines can exceed 3000°F. The engines must be cooled; otherwise, certain components such as pistons, valves, and cylinder heads suffer extreme damage. If the heat is not controlled, the engine risks detonation, loss of performance, and poor emissions. Controlling the temperatures protect the cylinder and allow oil to maintain a protective film on the surfaces and maintain lubrication. In addition, engine oil deteriorates as temperatures rise. Even when the oil appears to be clean, it may be experiencing deterioration. Further, the proper low ash oil helps protect the engines as well. Never use diesel engine oil in the place of an approved CNG oil.
Engines are designed as a system of components, and failure to use approved parts and follow approved maintenance schedules can do harm to the engine that may not be readily visible to the eye. For example, the use of poorly made spark plug wires can cause misfires, which raises heat. The installation of undersized catalytic converters and restrictions exceeding the manufacturers’ recommendations create additional heat and backpressure, and damage additional components like the turbocharger. Heat often localizes on the base of the cylinder head between the intake and exhaust valves, in an area called the valve bridge. Diesel engines often suffer cracks in these areas due to the high heat and high pressure. Manufacturers often use grey iron cylinder heads that can become stressed to their limits. The application of alternative fuels often exacerbates the effect of high temperatures on the valve bridge. Premature failure of the spark plugs is likely noticed as well.
CNG One Source has carefully studied the thermal characteristics of natural gas engines and has incorporated several small improvements to control heat. Again, there is no short cut to reducing temperatures by 200° if the vehicle is already equipped with the proper components. However, if improper components are installed, temperatures can raise by 200°F to 500°F very quickly.
A conversion “kit” installation is NOT merely replacing existing parts with parts in the kit, but requires following the proper installation procedures, which includes determining the proper design, size and operation requirements of the cooling system to successfully transfer heat from the engine. This includes consideration of a number of components including the water jacket, the oil cooler, the radiator, fan and intercooler, as well as the water pump and other miscellaneous components in order to insure safe operating temperatures. There are many resources available to provide for superior cooling characteristics. The installation center must install the correct cooling system. Hiring an engineer to determine the correct design is an option, but may not be necessary. Coolant manufacturers and radiator manufacturers are often valuable resources as are highly experienced engine mechanics.
The water jacket is a series of cavities that carry coolant throughout the engine. Heat is transferred from the engine to the coolant, and is carried away to the radiator. Water is one of the most effective means to transfer heat away from an engine. However, water boils at a low temperature of 212°F, and water vapor is extremely poor at protecting the engine. Therefore, in essence, 212°F is the temperature at which engine failure begins. Fortunately, there are methods of increasing the temperature to delay engine failure, which include increasing the pressure on the radiator cap, or employing a different type of coolant. Coolant flows through the passages of the engine block and head to remove heat. In natural gas engines, the combustion chamber requires cooling, and spark plug bosses are cooled by coolant flowing through the head.
The re-use of Torque To Yield bolts is not recommended, as they may be stretched past their tolerances, and the head gasket may leak as a result. In addition, the increased heat from natural gas engines create higher thermal stresses, and the stretched TTY bolt, along with higher pressures, may cause a failure as a result of the action. The manufacturer designed the passages in the head to allow for adequate coolant flow; however, because alternative fuels often operate at much higher temperatures, improved cooling is required. Scaling, improper coolant levels, aged coolants, and poor coolant choices can also result in premature engine failure. Finally it is very important to pressure test the radiator and the repowered cylinder head prior to installation. Otherwise, the operator may experience premature failure by symptoms such as leaking injector cups, water and foam in the oil, and white smoke coming from the exhaust.
No comments:
Post a Comment