一、 Energy Saving & Cost Reduction
  With the development of petroleum industry and the update of drilling equipment, the demand of industrial power has been increased since 21st century. However, the restriction of industrial power, because of the shortage of energy source, has been reinforced too. Natural gas as one dual fuel, its cost is lower and more environmental friendly than diesel. And it just need simple processed to fulfill the engine. The dual fuel control system developed by our company use natural gas as the main fuel rather than diesel, and natural gas hold above 70% of the total fuel. In that way, it can reduce the cost of power generation to maximum profit. At the same time, it can cut down the emission of some harmful substance to improve the environment around us.
二、 The Advantages of SDNE TECH Dual Fuel Engine/Generator Sets
1. Saving diesel consumption to reduce the cost effectively. When the dual fuel generator set is working, the normal power is the same as diesel generator, so as power performance. In high load condition, the replacing rate of natural gas can up to 70% in total fuel.  
2. Without natural gas, the generator can run with diesel only, and do not influence on normal running.
3. Reducing the emission of exhaust gas to improve the air cleanness and human living environment.
4. Adopted the mature and stable engine to modify the generator, so it is both reliable in quality and low in maintenance cost.
5. Dual fuel system is in high control accuracy and simple operation with low maintenance cost. 
三、 The Basic Configuration
1. Structure Development:
Dual fuel generator is modified from the diesel generator set, the original engine and the fuel supply system do not change, just need to add gas supply system. The gas supply system contains two parts: gas supply and gas control.
1) Gas supply includes high-pressure reducing valve, outage solenoid valve, low-pressure regulating valve, natural gas control valve and mixer etc.
   This system consists of natural gas supplied system, diesel supplied system and electronic control system.
  a) Natural gas supplied system
  As shown in the figure, natural gas supplied system adopt the method that premix air and natural gas. The gen set usually supply natural gas with low pressure (2-5bar). The pressure reducer lowers the pressure to 0.5-0.2bar, and the air inflow is controlled by flow control valve.   Air from the air filter is mixed with natural gas in the mixer and then go through the supercharger and intercooler and enter the inlet manifold, finally work in air cylinder separately.
  b) Diesel supplied system
  Almost remain the original diesel supplied system, besides adopting electronic governor instead of mechanical governor.
  c) Electronic control system
  Electronic control system mainly consists of dual fuel controller, temperature-pressure speed sensor, integrated actuator and wiring harness. Based on this system, working condition (such as starting, idle speed, rated speed and overspeed) can be judged. The working mode can be shifted rapidly and conveniently between pure diesel mode and dual fuel mode. Other functions are as follows: governing the electronic speed, correcting MAP (including gas volume, diesel oil capacity and substitute rate), controlling parameter online and troubleshooting.
四、 Principle of Diesel-CNG system
1. Natural gas enters the high-pressure tank and through high-voltage tube which can reduce the voltage from 20MPa to 0.1MPa, and then enters outage solenoid valve. Next it will come to the low-pressure regulating valve and experience pressure reduced again (0~0.5kPa), and then it will enter mixer from natural gas control valve. Natural gas is mixed with air according to a certain proportion in the mixer. The gas mixture will flow in air inlet duct and finally enter every air cylinders after pressurization and cooling. When the engine break down or shut down, solenoid valve will stop supplying natural gas automatically. Diesel is supplied by the original generator’s oil supply system, and the quantity supplied is automatically adjusted by mechanical governor or electronic speed controller of the high-pressure oil pump. Under the condition of the same load, the speed controller will reduce the capacity of diesel supplied because natural gas participates in working. The mixer adopt Venturi throat mixing method, and the intake of natural gas will automatically track the intake of air to a certain extent. The mixer works together with the pressure reducing valve system to ensure that the engine gets the most ideal air-fuel ratio in each working condition and improve the operational process of the engine.
2. The Rationale of Gas Control System
The gas control system of dual fuel engine adopts dual fuel controller. The controller collects the voltage and temperature of the engine intake duct, and then calculate the load signal of the engine. According to the revolving speed and the load signal, the parameter of MAP graph of gas regulating valve can be determined in controller’s internal storage. And the controller issues instructions to actuator constantly and control the flow area of natural gas. The opening of gas regulating valve can be decided by the revolving speed and the load signal in real time, thus the engine is running at its best all the time.
Figure 1. Schematic of dual fuel system (diesel/natural gas)

  As is shown in the above figure, this system was designed to transform the present diesel engine based on mechanical governor or electronic speed controller solely. It can be updated to dual fuel system by adding gas fuel supply system and controlling the quantity of diesel. The working mode can be shifted between diesel mode and dual fuel mode by fuel selection switch. While dual fuel mode can be shifted to diesel mode automatically. When the generator is working under the diesel mode, the dual fuel control module close the natural gas controlling, and at this time it is working as the same as the original diesel generator. When the generator is working under the dual fuel mode, the quantity of diesel is limited to a fixed amount (usually is 20%-30% of full capacity), and the rest are natural gas.
五、 The Safe Reliability of Generator Set
1. We adopt all-digital controller, which is reliable and accurately, thus the system can work at its best in real time.
2. When the engine is switched to pure diesel mode, the solenoid valve will stop supplying natural gas automatically.
3. Under the same load, the temperature of the cylinder of dual fuel mode is 20℃ to 30℃ lower than pure diesel mode, but the exhaust temperature is nearly the same, so the radiator of the original diesel generator can also exert a cooling effect.
4. Dual fuel engine came into being by adding a dual fuel system but not changing the major components of the original diesel generator, thus the quality of the whole engine can be guaranteed.
六、 The Basic Indexes of SDNE TECH Dual Fuel Engine/Generator Sets
1. The substitution rate of diesel is 60% to 75%
2. The power can reach to the level of diesel generator
3. The operation is generally the same as diesel generator
4. The transforming is simple, the cost is low and the period of returns on investment is short.
七、 Economic Analysis on Dual Fuel Engine/Generator Sets (Natural Gas & Diesel)
The model of engine: 500KW Engine/Generator Sets (12V190)
Service hours: 5h
The fuel consumption (pure diesel): 125L/h
Local price of gas: 3.7 yuan/m3
Local price of fuel: 7.5 yuan/L
The average substitution rate of diesel: 70%
The total cost of pure diesel engine: 125*5*7.5=4687 yuan/day
The cost of dual fuel engine:
    the cost of diesel: 125*7.5*30%*5=1406 yuan/day
    the cost of natural gas: 125*3.7*70%*1.15*5=1861 yuan/day
    the total cost of dual fuel engine= the cost of diesel the cost of natural gas=1406 1861=3267 yuan/day
Economic efficiency: the cost of pure diesel-the cost of dual fuel=4689-3267=1420yuan/day=1420*30=42600yuan/month=42600*12=511200 yuan/year
八、 The Configuration Instructions of SDNE TECH Dual Fuel Engine/Generator Sets
1. Engine: chosen from 190, Cummins, Yuchai and Weichai
2. Generator: chosen from Siemens or domestic advanced generator
3. Gas control system: we adopt SDOTX39 dual fuel system
4. Power and output control system: COMAP
九、 Major technical indexes of dual fuel control system
1. SDOT9200 dual fuel controller
Power: 24VDC
Revolving speed: 0.5V~120VRMS
Voltage: 0~5VDC
Temperature signal: 0~44 KΩ
Substitution rate setting: ＜85%
Drive output outage valve: 1A/24VDC
Position signal output: 4~100mA
Operating temp: -30℃~ 70℃
Relative humidity: ＜95%
2. Integrated actuator
Model: SDOT960
Power: 24VDC
Output current: persistent 10A to the peak of 20A, last 2s
Output torque: ＜8Nm
Operating temp: -40℃~ 100℃
Relative humidity: 95% in 38℃
Diameter: Φ65-Φ85
3. Mixer: Φ121XΦ80
4. Sensor
A. speed sensor (C181580)
DC resistance: approximately 350Ω
Signal frequency: 100Hz～10KHz
Screw thread: Φ1815
B. pressure-temperature sensor (102750)
Voltage range: 0~200KPa
Output voltage: 0~5VDC
Temperature range: -40℃~ 120℃
Output resistance: 0~44KΩ
十、 Notes for using dual fuel control system
1. Strictly observe the operation instruction to install gas pipeline and other control devices in case of natural gas leaking.
2. Use single speed sensor to provide speed signal for dual fuel device.
3. Use external control switch to control gas’s on and off.