Diesel Locomotives

Figure 4: Diagram of a traditional diesel engine governor. It consists of a rotating shaft, driven by the diesel
engine. A pair of flyweights are linked to the shaft and they rotate as it rotates. The centrifugal force caused by
the rotation causes the weights to be thrown outwards as the speed of the shaft rises. If the speed falls the
weights move inwards. The flyweights are linked to a collar fitted around the shaft by a pair of arms. As the
weights move out, so the collar rises on the shaft. If the weights move inwards, the collar moves down the
shaft. The movement of the collar is used to operate the fuel rack lever controlling the amount of fuel supplied
to the engine by the injectors. Modern engines use electronic governors. Diagram Author.
Fuel Injection
Ignition is a diesel engine is achieved by compressing air inside a cylinder until it gets very hot (say C, almost F) and then injecting a fine spray of fuel oil to cause a miniature explosion. The explosion forces down the piston in the cylinder and this turns the crankshaft. To get the fine spray needed for successful ignition the fuel has to be pumped into the cylinder at high pressure. The fuel pump is operated by a cam driven off the engine. The fuel is pumped into an injector, which gives the fine spray of fuel required in the cylinder for combustion. Fuel Control
In an petrol engine, the power is controlled by the amount of fuel/air mixture applied to the cylinder. The mixture is mixed outside the cylinder and then applied by a throttle valve. Ina diesel engine the amount of air applied to the cylinder is constant so power is regulated by varying the fuel input. The fine spray of fuel injected into each cylinder has to be regulated to achieve the amount of power required. Regulation is achieved by varying the fuel sent by the fuel pumps to the injectors. The amount of fuel being applied to the cylinders is varied by altering the effective delivery rate of the piston in the injector pumps. Each injector has its own pump, operated by an engine-driven cam, and the pumps are aligned in a row so that they can all be adjusted together.
The adjustment is done by a toothed rack (called the "fuel rack) acting on a toothed section of the pump mechanism. As the fuel rack moves,
so the toothed section of the pump rotates and provides a drive to move the pump piston round inside the pump. Moving the piston round,
alters the size of the channel available inside the pump for fuel to pass through to the injector delivery pipe. The fuel rack can be moved either by the driver operating the power controller in the cab or by the governor. If the driver asks for more power,

the control rod moves the fuel rack to set the pump pistons to allow more fuel to the injectors. The engine will increase power and the governor will monitor engine speed to ensure it does not go above the predetermined limit. The limits are fixed by springs (not shown) limiting the weight movement.
Engine Control Development
So far we have seen a simple example of diesel engine control but the systems used by most locomotives in service today are more sophisticated. To begin with, the drivers control was combined with the governor and hydraulic control was introduced. One type of governor uses oil to control the fuel racks hydraulically and another uses the fuel oil pumped by a gear pump driven by the engine. Some governors are also linked to the turbocharging system to ensure that fuel does not increase before enough turbocharged air is available. In modern systems,
the governor is electronic and is part of a complete engine management system.
Power Control
The diesel engine in a diesel-electric locomotive provides the drive for the main alternator which, in turn, provides the power required for the traction motors. We can see from this therefore, that the power required from the diesel engine is related to the power required by the motors. So, if we want more power from the motors, we must get more current from the alternator so the engine needs to run faster to generate it. Therefore, to get the optimum performance from the locomotive, we must link the control of the diesel engine to the power demands being made on the alternator.
In the days of generators, a complex electro-mechanical system was developed to achieve the feedback required to regulate engine speed according to generator demand. The core of the system was a load regulator, basically a variable resistor which was used to very the excitation of the generator so that its output matched engine speed. The control sequence (simplified) was as follows. Driver moves the power controller to the full power position
2. An air operated piston actuated by the controller moves a lever, which closes a switch to supply a low voltage to the load regulator motor.
3. The load regulator motor moves the variable resistor to increase the main generator field strength and therefore its output.
4. The load on the engine increases so its speed falls and the governor detects the reduced speed.
5. The governor weights drop and cause the fuel rack servo system to actuate.
6. The fuel rack moves to increase the fuel supplied to the injectors and therefore the power from the engine.
7. The lever (mentioned in 2 above) is used to reduce the pressure of the governor spring.
8. When the engine has responded to the new control and governor settings, it and the generator will be producing more power.
On locomotives with an alternator, the load regulation is done electronically. Engine speed is measured like modern speedometers, by counting the frequency of the gear teeth driven by the engine, in this case, the starter motor gearwheel. Electrical control of the fuel injection is another improvement now adopted for modern engines. Overheating can be controlled by electronic monitoring of coolant temperature and regulating the engine power accordingly. Oil pressure can be monitored and used to regulate the engine power in a similar way.
Cooling
Like an automobile engine, the diesel engine needs to work at an optimum temperature for best efficiency. When it starts, it is too cold and,
when working, it must not be allowed to get too hot. To keep the temperature stable, a cooling system is provided. This consists of a water- based coolant circulating around the engine block, the coolant being kept cool bypassing it through a radiator. The coolant is pumped round the cylinder block and the radiator by an electrically or belt driven pump. The temperature is monitored by a thermostat and this regulates the speed of the (electric or hydraulic) radiator fan motor to adjust the cooling rate. When starting the coolant isn't circulated at all. After all, you want the temperature to rise as fast as possible when starting on a cold morning and this will not happen if you a blowing cold air into your radiator. Some radiators are provided with shutters to help regulate the temperature in cold conditions.
If the fan is driven by a belt or mechanical link, it is driven through a fluid coupling to ensure that no damage is caused by sudden changes in engine speed. The fan works the same way as in an automobile, the air blown by the fan being used to cool the water in the radiator. Some engines have fans with an electrically or hydrostatically driven motor. An hydraulic motor uses oil under pressure which has to be contained in a special reservoir and pumped to the motor. It has the advantage of providing an inbuilt fluid coupling.
A problem with engine cooling is cold weather. Water freezes at Cor F and frozen cooling water will quickly split a pipe or engine block due to the expansion of the water as it freezes. Some systems are "self draining" when the engine is stopped and most in Europe are designed to use a mixture of antifreeze, with Gycol and some form of rust inhibitor. In the US, engines do not normally contain antifreeze, although the new GM EMD "H" engines are designed to use it. Problems with leaks and seals and the expense of putting a 100 gallons (378.5 litres) of coolant into a 3,000 hp engine, means that engines in the US have traditionally operated without it. In cold weather, the engine is left running or the locomotive is kept warm by putting it into a heated building or by plugging in ashore supply. Another reason for keeping diesel engines running is that the constant heating and cooling caused by shutdowns and restarts, causes stresses in the block and pipes and tends to produce leaks.
Lubrication
Like an automobile engine, a diesel engine needs lubrication. In an arrangement similar to the engine cooling system, lubricating oil is distributed around the engine to the cylinders, crankshaft and other moving parts. There is a reservoir of oil, usually carried in the sump,
which has to be kept topped up, and a pump to keep the oil circulating evenly around the engine. The oil gets heated by its passage around the engine and has to be kept cool, so it is passed through a radiator during its journey. The radiator is sometimes designed as a heat exchanger, where the oil passes through pipes encased in a water tank which is connected to the engine cooling system.

The oil has to be filtered to remove impurities and it has to be monitored for low pressure. If oil pressure falls to a level which could cause the engine to seize up, a "low oil pressure switch" will shutdown the engine. There is also a high pressure relief valve, to drain off excess oil back to the sump.
Sources:

The Railroad, What it is, What it Does by John H. Armstrong, 1993, Simmons Boardman Books Inc BR Diesel Traction Manual for Enginemen,
British Transport Commission, 1962; BR Equipment, David Gibbons, Ian Allan, 1986 and 1990; Modern Railways International Railway
Journal; Railway Gazette International Mass Transit Trains Magazine The Railway Technical Website 2019