Technical Info
Introduction
The Diesel On Gas dual fuel system can be fitted to turbo-charged diesel engines and provides a means of substituting diesel fuel with alternative fuels such as LPG and CNG. The system uses a combination of proven automotive gas components with an electronic control system to provide an efficient and reliable alternative fuel delivery. The system can be fitted without significant engine modifications. The Electronic Control Unit (ECU) communicates with a number of sensors monitoring temperatures and pressures to ensure the correct amount of fuel is delivered under all conditions. The system monitors the sensors and will shut the alternative fuel system down if the engine operates outside the design parameters of the system.
The level of gas substitution depends on a variety of factors with a maximum value of up to 50% and average values of up to 30% achievable.
The level of gas substitution is maximized when an engine can be operated continuously at around 60% of its rated maximum power output. It is important to note that applications with significantly variable engine load will result in reduced gas substitution rates.
System Diagram
Components
Fuel Tank and High Pressure Fuel Supply
The alternative fuel is generally stored in a suitable tank on the vehicle (for stationary engines the fuel supply can be taken from a fixed distribution system). The equipment for the storage and high pressure fuel supply is common to LPG/CNG conversions of petrol fuelled vehicles. Installation is as for a petrol to LPG conversion or petrol to CNG conversion, that is, in accordance with AS1425 or AS2739.
Gas Converter or Regulator
As for the high pressure fuel supply the converter or regulator on the Diesel On Gas system will be similar to those used on petrol engine conversions. For LPG the converter takes the pressurized liquid and allows it to vaporize and reduce pressure to about atmospheric pressure. To do this effectively, the converter must be heated. This is generally achieved through running the engine’s cooling water through the converter. For CNG, as the fuel is already in gaseous phase, the regulator reduces its pressure to around atmospheric before the fuel is introduced to the Gas Mixer. The converter/regulator is installed in the engine bay.
Vapor Control Components
After passing through the converter or regulator the fuel is delivered to the gas mixer through the vapor line. In the vapor line a shut off valve and a variable flow valve are installed to control the vapor flow. The vapor line pressure is also monitored to ensure any problem with the converter or regulator is quickly identified.
Gas Mixer
The Gas Mixer meters and mixes the LPG/CNG vapor with air passing through the vehicle’s air intake system. The fuel/air mix is then compressed in the turbo charger and so delivered to the combustion chamber. The design of the mixer is patented. The main benefits of the Diesel On Gas mixer are that high levels of fuel substitution are achievable, it produces no measurable flow restriction in the intake ducting and the mixer uses engine boost pressure to meter the LPG/CNG flow. The mixer unit is installed between the air cleaner and the turbo-charger. Due to the size of the mixer unit its installation needs careful planning with appropriate ducting components sourced prior to commencing any dismantling work.
Control System
The basic control system consists of an Electronic Control Unit and electronic Variable Valve Control connected to a number of sensors and valves.The Electronic Control Unit (ECU) monitors all sensors installed in the system. It adjusts the gas supply to suit the operating condition of the engine. In addition to the external inputs listed below the ECU monitors alternator voltage and monitors and logs the temperature inside the electronic housing.
The ECU is controlled by patented firmware. Installers can log on to the ECU program using a laptop computer and make adjustments to certain operating parameters or carry out simple diagnostic procedures. The program is password protected to avoid unauthorized modifications.
When using Biodiesel in a Catepillar engine and in conjunction
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Inputs
- On/Off Switch
Is normally combined with a gas tank contents gauge. Provides the control interface for the operator to enable or disable the gas substitution system. - Vapor Pressure
The sensor is physically mounted inside the ECU. Should an excess pressure be sensed (possible cause - gas converter failure) the system is shut down. If the system shuts down due to a vapor pressure problem it needs to be password reset through PC communication with the ECU. - Intake Manifold Boost Pressure
The sensor is physically mounted inside the ECU. It is used as an indication of the power being produced by the engine. The reading is modified within the ECU programming to allow for changes in intake manifold temperature. - Intake Manifold Temperature
The ECU uses the temperature signal to adjust the intake pressure reading for reduced air density due to temperature increase. - Exhaust Temperature
The sensor is fitted to the exhaust system after the turbo charger. The ECU uses the signal to assess the power being produced by the engine relative to what is considered to be its maximum. Threshold is set at 90% of maximum allowable exhaust temp (as per manufacturer). In the absence of specific manufacturer's data the ECU is set to shut down the fuel supply if the exhaust temperature exceeds 600°C. - RPM Sensor
It is fitted to trucks primarily to avoid engine overrun when changing gears. - Gas Converter Temperature
Temperature is monitored in order to ensure minimum required vaporization temperature is reached before gas is switched on by the ECU. Gas converter temperature must be above 45°C. It is required on trucks as high gas flow rates are encountered which can cause the converter to freeze up. - Exhaust Braking Activated (truck only)
In trucks with an engine braking or an exhaust braking system it is desirable that the alternative fuel substitution be switched off when the exhaust or engine braking system is switched on.
Outputs
- HP Das Shut-Off Valve (2)
The two valves are connected to the same ECU output. The output switches the valves on and off as required. - Vapour Shut-Off Valve
This valve is shut off when the fuel substitution is not required. - Variable Flow Vapour Valve
The ECU controls the Variable Flow Vapour Valve through the Variable Valve Controller (VVC). The valve position is adjusted by means of a stepper motor that allows it to be opened to any position between closed and fully open. - Gas Indicator Light
Is switched on by the ECU when substitution is activated.
Options
- Power Control Unit
The power control unit is an additional controller used when the engine incorporates electronic fuel injection control. The unit is connected between the OEM Electronic Controller and the engine's MAP sensor. - Telemetry System
Allows for remote communication with the fuel substitution system. Through telemetry the ECU settings can be modified by telephone. Data logged by the ECU can be retrieved remotely also.
