The main problem with a diesel engine is - getting it to start. The problem is compounded if
a. The engine happens to be an indirect injection model
b. The temperature is near or below freezing point
c. The engine is to be started with fuel other than diesel.
To overcome this problem most diesel engine vehicle manufacturers provide an engine heating system and/or a provision to start the engine with ether or petrol and then change over to diesel. Electric heating systems can be auto or manual. Electrical heating of the diesel engine is done in several ways. Two of the most commonly used systems are heating the chamber with glow plugs and heating the intake air with an electric air heater placed in the intake manifold.
In a manual heating system, a push button is pressed to make the dashboard mounted glow indicator to show the amount and duration of glow being transmitted to the chambers through a series of glow plugs. The advantage of this system is that there is no complicated electronic glow control system. However the disadvantage is that you try and heat on a hunch. If the button is kept pressed for a longer time than necessary, the battery will get drained and the life of the glow plugs will get reduced.
In an automatic engine heating system through glow plugs, the heating is started automatically as soon as the ignition switch is turned on. The CPU controller (timer) either senses the actual temperature of the engine through a sensor mounted on the engine block or in the cooling water jacket, or it senses indirectly with an internal device in the controller (timer). On the basis of the `feed back' of the sensor, the controller (timer) automatically determines the amount of heat duration to be given to the glow plugs. At the end of the required heating cycle the controller gets automatically switched off and indicates that pre-heating is over and the engine is ready for starting. The controller waits for the next starting of the engine. The advantage of this system is that the operation is fully automatic whenever the engine is started and heating cycle automatically operates as per the required time. This conserves battery power and increases the life of glow plugs. Further it eliminates `white smoke' which causes harmful air pollution. This kind of automatic system is more advantageous than intake air heating system, which can not pre-heat the chambers causing heating inefficiency. The air heater is also far more costly than glow plugs and replacement is difficult. It also consumes more energy than direct heating through glow plugs.
Most manufacturers of indirect or direct injection diesel engines are incorporating automatic engine heating systems of 12 or 24 Volt glow plugs but some are also using a quick glow system through 5.6V or 9 V systems for quick glow of glow plugs. With the quick glow system the controller becomes more complicated and expensive. Therefore the standard has become a normal heating time of around 7/8 Sec. at 20 Deg. C. The time-heat curve has been calibrated in the controller to vary the heating time automatically as per the engine temperature. In other words the heating time will get reduced to a second when the engine is in hot condition whereas the time will extend to as long as 30 Sec when starting conditions are extremely cold.Additionally, for extremely cold climates, manufacturers are providing simultaneous heating during cranking after pre-heat period is over and again post heating time after the diesel engine has started. This simultaneous & post heating eliminates the emission of `white smoke' due to nil or partial combustion of the fuel, in extreme cold climates. However to retain the prospect of future parts sales, manufacturers do not allow interchangeability of the heating systems between different vehicles. This escalates prices and often local technicians do not know how to check, replace and calibrate these systems.