How does a Western Diesel Locomotive work?
A diesel engine works by internal combustion. Fuel is sprayed into the cylinders with air and compressed by a piston. If you compress a gas, it produces heat. In a diesel engine, this heat is sufficient to ignite the fuel, which explodes. Unlike a petrol engine, there is no sparking plug. This explosion produces an expansion of gases within the cylinder, which forces the piston down. The piston is linked to a crankshaft, which converts the up, and down motion of the piston into a turning motion known as torque.
The Western locomotive has two 65 litre Maybach MD 655 diesel engines each driving a Voith hydraulic transmission, which turn the wheels via a gearbox. The cylinders are arranged in a V formation driving a common crankshaft. The Maybach diesel engine has 12 cylinders and produces 1380 hp at 1,500 rpm. Maybach diesel engines were also used in marine installations such as motor torpedo boats and fishing boats.
The Maybach diesel engine operates on a four-stroke cycle: that is two up strokes and two down strokes. An inlet valve and an outlet valve are operated from a camshaft and control the air into the cylinder and the exhaust gas out.
The sequence is as follows:-
First stroke-Induction. This begins as the piston commences the down stroke with the inlet valve open. As the piston commences downward, it draws air past the open inlet valve into the cylinder. The exhaust valve is closed at this stage.
Second stroke-Compression. When the piston has completed the down stroke, the inlet valve closes, and as the exhaust valve is already closed, the air contained in the cylinder is trapped. The revolving crankshaft pushes the piston up and as it rises, the air trapped in the cylinder is compressed up into the combustion chamber. As the air is compressed, it becomes extremely hot.
Third stroke-Power. With the valves still closed, fuel oil is sprayed through an injector into the top of the cylinder at the point of greatest compression and heat. The heat from the compressed air causes the fine oil to ignite and greatly expand in volume. This forces the piston down the cylinder.
Fourth stroke-Exhaust. At the end of the power stroke, the exhaust valve opens and during the following up-stroke of the piston the waste gases are pushed past the valve and out of the engine.
A turbo-charger is used in order to obtain the maximum power from the engine. This is a device, which contains a turbine that sucks in air and forces it into the inlet valve of the engine. The turbo-charger is driven from a turbine powered by the exhaust gases of the engine.
To keep the engines and turbo-chargers cool, the locomotive has large fans mounted in the roof. These draw air through the louvres in the body-side and through the radiators mounted above the engines. The turning action of a diesel engine cannot be linked directly to the wheel. It has to be controlled so that the locomotive can start from rest with a train and cope with different gradients and loads. This is achieved on a Western locomotive using a hydraulic transmission. Most locomotives nowadays use diesel electric transmission where the diesel engine turns a generator and the power produced drives electric motors, which turn the wheels.
In a diesel hydraulic locomotive, there is a torque converter, which is rather like a hydraulic pump revolving inside a housing filled with oil. It has three main parts, of which two rotate and one is fixed. Each part consists of a ring with specially shaped blades. The blades are curved to control the direction of the flow of oil. The three parts of a torque converter are the impeller (a centrifugal pump), the turbine wheel (or driven wheel) and the fixed guide wheel (or reaction wheel). The diesel engine drives the impeller and its power is passed on to the oil in the converter. The oil is impelled by the impeller blades onto the turbine wheel blades, causing the turbine wheel to rotate.
The above photograph shows the relatively small and compact size of a hydraulic transmission.
The turbine wheel is connected by a shaft to the locomotive wheels. When the turbine wheel rotates, the locomotive wheels rotate. The oil is returned by the turbine wheels to the impeller, passing through the blades of the fixed guide wheel which adjust the angle of the flow of oil to the impeller. The oil is pumped around the circuit repeatedly.
The advantage of a diesel hydraulic system was its lightweight construction. Also, the torque converter is so designed so that the lower the speed, the greater the pulling power. It also provides a shock free drive between the engine and locomotive wheels over the whole range of engine power.