Home page
What is a turbotrain?
What is a gas turbine?
   Merit demerit
   Torque details
__More power!
__More speed!
__Miracle in non-electrified line
__ Oil crisis
Turbo train in Japan
  Background for the birth
    Primary source1
    Primary source2
    Primary source3
    Primary source4
    Primary source5
    Primary source6
    Primary source7
    Primary source8
    Primary source9
    Primary source10
    Primary source11
  Revealed problems
Gas turbine advancement
  Facts M1 Abrams revealed
  Second generation of turbines
   Challenge to diesels
Trends of turbo trains
  ALPS project
  Low emission locomotive
 Performance of turbo train
 Is M1 power pack available?
 Effects of 4 speed transmission
  JetTrain simulation
  JetTrain 300 km/h operation
  EMU versus Turbo train

Does the 4 speed transmission improve the performance?


M1 Abrams tank has 4 speed transmission. This mechanism makes up for the 2 shaft gas turbine's insufficient torque at the low rpm range for rail applications.
To demonstrate effects of the 4 speed transmission,  design turbo trains with the four-speed gear box. The consist of each train is same as that of previously designed.
next is performance curves of them. 

The acceleration force at low speed range dramatically improves and even the 2M4T turbo train achieves the performance close to the DMU made up of all motive cars.
The performance curve becomes more close to an ideal curve.

The four speed transmission also improves the fuel consumption because the turbine can spin at the optimal speed by changing gears when the train is running at the low speed.
The high acceleration reduces the powering time and the optimal engine operation increases the efficiency. As a result, the total fuel consumption decreases.

To understand this feature, notchman mini has a good function. It is generally called the efficiency distribution chart or map. This is a color coded map of the combined efficiency of the engine and the drivetrain as a function of the train speed and the output. In this map, the white parts are most efficient and the black parts are worst.  

The next is the efficiency distribution map of the single speed direct drive turbo train powered by the simple cycle two-shaft gas turbine. The high efficiency is available only in the limited area and the lower the speed and load, the worse the efficiency is. The optimal rpm of the aero-derivative gas turbine is designed as the maximum rotation speed and if such a engine used for the vehicle application, the most efficient speed equals to its maximum speed and in most cases, not suitable from the point of view of fuel consumption.

As described in the user's manual of notch man mini, the maximum rpm of gas turbines designed for vehicles was set  to 120 to 160 percent higher than its optimum rpm. AGT1500 can spin 120 percent rpm and Chrysler turbine car had the engine that could spin 160 percent rpm against its optimum point. This feature improves performance of the single gear direct drive. The paid version of notch man mini has the function to simulate this kind but the free version does not allow it. 

On the other hand, diesel engines demonstrate a good efficiency in the wide area of the speed and the output. The efficiency of the hydraulic converter is not good enough but after the engine is directly coupled, the efficiency is high and still maintains high in the area of low rpm and the partial load as shown below.

The recuperation of the gas turbine improves the efficiency at the low load of the engine and 4 speed gear box improves the efficiency at the low speed of the train as shown below.

The simulated route is the same as the route used in the previous scenario 1. The performance of the simplest turbo train

The next running curves well demonstrate the effect of 4 speed gear transmission. The low power 2M4T turbo train runs all motive DMU very close.

The improvement is also seen when the distance between stations is short.

The required time is shown below.

The next table shows the fuel consumption. About 20 % reduction of the fuel consumption is achieved by 4 speed gear drivetrain.

Consist single speed four speed
2M4T 1232.36 kg 1032.76 kg
3M3T 1399.42 kg 1214.03 kg
4M2T 1556.47 kg 1374.14 kg
DMU 6M   1101.54 kg

The traveling time reduction and the fuel savings are simultaneously achieved. Especially in 2M4T turbo train, the required time is a few minutes longer than 6M DMU but the fuel consumption is less. This is due to the turbine's light weight and high accelerating performance.. 

The next is the simulation result of scenario 2 done in previous page. The same tendency is seen in this simulation.

Consist fuel consumption
2M4T 1200.07 kg
3M3T 1458.59 kg
4M2T 1689.78 kg
DMU 6M 1244.28 kg


Go to the top of this page