Ignition Differences between Gas and Diesel Engines

One of the questions that prospective owners of engine powered equipment typically ask themselves, is which type of power motor is preferred? Should machinery with a diesel engine be chosen, or machinery with gasoline engines is given preference? The answer to that question varies with many parameters, one of which is described below. One major difference between the diesel and gasoline engines is the manner in which fuel combustion occurs. With the gasoline engine, there are a few mechanisms that are working at approximately the same time. The basic combustion process is that an appropriately mixed air to fuel vapor is drawn into the combustion area above the piston head, (located in the cylinder block), and then the spark plug provides a spark for ignition to occur. This process is a rapid explosive exothermic reaction. The rapidly expanding gases push the piston downward, turning the crankshaft via the connecting rod, and hence motive engine power. The spark ignition process begins with power being supplied from the battery. This 12v (or 24v) power is fed into an ignition coil, which increases the voltage, while at the same time reducing its current. The result is a high potential difference that is now delivered to the distributor.


The distributor is a combination of electrical and mechanical components, however, since it’s not under discussion here, its function is simply to deliver the high potential difference from the ignition coil, to the spark plugs, via the spark plug wires (or leads), in a timely fashion. None of the above components, namely the ignition coil, distributor, spark plugs, and spark plug leads are found in the diesel engine. Combustion in the diesel engine occurs in a slightly different manner. The air to fuel mixture is first pushed into the cylinder combustion area, and then the valve closes at the same time the piston is moves upwards. The air / fuel mixture is highly compressed in the combustion chamber, to such as extent that the mixture simply ignites by itself without the need for an external ignition source like that provided by a spark plug. Therefore, the first advantage of the diesel engine over the gasoline engine is simply less components to fail, and therefore less maintenance issues.


The air to fuel mixture in gasoline engines occurs in a carburetor in older tractor engines. Modern gas engines use a fuel injection system. All diesel engines uses fuel injector pumps and fuel injectors as part of the fuel system that provides fuel to the engine. This fuel is injected directly into the combustion chamber, just before the piston reaches TDC (Top Dead Center) position. Easy Tractor Parts is a premium aftermarket provider of Old Ford Tractor Parts and Antique Ford Tractor Parts