Open Rails Basic Diesel Parameters
Aim - this section describes the basic "optimal" settings for diesel related parameters in Open Rails (OR) ENG files.
This page references information for the British Rail Class D16/2 (#10203) diesel electric locomotive which has been used as a demonstration and test model. The documents indicated in the Useful References at the bottom of this page were used as the principal reference sources. A diesel test model based upon this locomotive has been configured for use in Open Rails.
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The Diesel locomotive as the name implies is driven by a diesel engine. The diesel engine, or prime mover, produces the power to drive the locomotive forward and pull the train. The power produced by the prime mover is transmitted to the driving wheels, by a number of different transmission systems including mechanical transmission, electric traction motors, or hydraulic drive systems. The diesel typically is cheaper to operate then a steam locomotive, and some of the other advantages include the fact that they can be operated in multiple units with a single driver, they can be started or stopped almost instantaneously compared to a steam locomotive which requires time to build up steam.
To understand the performance of a diesel locomotive the following two subjects will be considered:
- Tractive Effort
For realistic performance it is important to set the Open Rails diesel parameters to calculate the correct values.
A British Railways Class D16/2 has been selected as an example of how to define a Direct Current (DC) locomotive, and is available from the test stock page.
The amount of force (or effort) available at the rail to drive the locomotive forward will be determined by the diesel engine (prime mover) and the transmission system which converts the mechanical enegry of the prime mover to an energy force at the rails. In the case of the BR Class D16/2, as it is a diesel electric DC locomotive, the prime mover drives a DC electric generator, which in turn supplies electricity to the DC traction motors which drive the locomotive wheels. Each of these elements suffer from some form of loss, which means that the full power of the prime mover, is not available to the rails for the diesel's tractive effort.
Reading the test report for the Class D16/2, we find the following information:
- Prime Mover - Typically most diesel locomotives are rated on the power of their prime mover, so in this case the Class D16/2 has a 2000hp prime mover. However some of its energy output goes into driving the locomotive auxiliaries, such as auxiliary generator, radiator fan, etc. Approximately 120 hp is used for the auxiliary equipment, which leaves approximately 1880 hp for tractive use (see pg 14 - item e).
- Generator - The generator has an effciciency of approximately 94%, thus the effective output from the generator is approximately 1767 hp (1309 kW) (see pg 22 - item e).
- Traction Motors and Gears - The traction motor and gears have an effciciency of approximately 88%, thus the maximum effort power available to be applied to the rail is approximately 1555 hp (1152 kW).
The overall effciency of the locomotive can be calculated by combining the last two items above together to get a value of 83%. Thus a value of approximately 80% can sometimes be used to calculate the maximum effective power available to be applied to the rails for a diesel locomotive.
In specifying a diesel locomotive it is quite common to define a design tractive effort curve against the locomotive speed. The diagram below shows an example of one.
The following points are worth noting from the diagram:
- Continuous Tractive Effort - indicates the continuous or constant force that can be maintained indefinitely on the wheels to drive the locomotive forward. Typically Force = Power / Speed. Thus as the speed increases the force will decrease, as shown by the red curve in the graph below. For our demonstration model, 30,000lbf @ 19.5 mph.
- Maximum Tractive Effort - is the maximum force that can be applied to the wheels without causing damage to the locomotive, or exceeding its adhesion limits. This force is shown by the blue curve in the graph below. For our demonstration model, 50,000lbf.
- Maximum Speed - is the maximum design speed that the locomotive can operate at, and is shown by the green line on the graph below. For our demonstration model, 90 mph.
The section below demonstrates some of the key diesel code, and shows how these values are configured into a standard ENG file.
Load Hauling Performance
Once the parameters are determined for the ENG file, load hauling performance tests should be undertaken to confirm that the locomotive performance is within acceptable bounds for the locomotive being modelled.
Often in test reports the Traction Draw Bar Tractive Effort (Traction DBTE) is used to describe the pulling power of the locomotive. This is calculated by considering the impact of the locomotive resistance, trailing load resistance, and gross weight ratio, on the tractive effort calculated above. A detailed explantaion of how to calculate this value can be found on pg 48 of the test report in the Useful References section below. This is the amount of force that is available to overcome the resistance offered by the trailing load behind the locomotive. The graph below shows the Traction DBTE for a diesel locomotive, as well as the trailing load resistance for a 300 ton train on various different gradients.
So for example, with a load of 300 ton the Traction DBTE will vary with speed as shown by the green curve. If the train is climbing a 1 in 80 gradient the trailing load resistance is shown by the red curve. The point where the two curves cross designates the "balancing speed", ie the maximum speed that the locomotive can travel when climbing a 1 in 80 grade with a 300 ton load.
Key Open Rails Parameters for Diesel Locomotives
The key parameters that impact upon the performance of a diesel locomotive are described on the following web page.
Sample Diesel Code
The code parameters shown below are those that are required to define a diesel locomotive within Open Rails. They should be set using known parameters so that the optimal accuracy of operation can be obtained.
A diesel test model with sample ENG files can be downloaded from the CTN test stock page.
When inserting values in these parameters it is recommended that you use the appropraite units of measure.
Comment ( *** General *** )
WheelRadius ( 0.5461m )
Sanding ( 25mph )
NumWheels ( 6 )
ORTSDriveWheelWeight ( 109.5t-uk )
Comment ( *** Diesel Engine *** )
Type ( Diesel )
MaxPower ( 1260kW )
MaxForce ( 222.411kN )
MaxContinuousForce ( 133.446kN )
MaxDieselLevel( 1180g-uk )
MaxVelocity ( 90mph )
MaxTemperature ( 120degF )
MaxOilPressure ( 90 )
DieselUsedPerHourAtMaxPower ( 75.2g-uk )
DieselUsedPerHourAtIdle ( 25.5g-uk )
DieselEngineIdleRPM( 450 )
DieselEngineMaxRPM( 850 )
DieselEngineMaxRPMChangeRate( 40 )
Comment ( *** Diesel Engine - Exhaust Effects *** )
DieselSmokeEffectInitialMagnitude( 1.7 )
DieselSmokeEffectMaxMagnitude( 2.2 )
DieselSmokeEffectInitialSmokeRate( 0.2 )
DieselSmokeEffectMaxSmokeRate( 10 )
Comment ( *** Electric Motor *** )
MaxCurrent ( 2600A )