New electronic gas carburetor from Continental Controls.
The emissions limits set by government agencies differ from region to region. The EGC 2 is designed to provide the best available control technology when used in conjunction with a properly sized three-way catalytic converter, allowing a properly operating engine to meet even the most stringent emissions requirements for gas engines. In addition, the carburetor is designed to improve fuel economy, according to the company.
"With the new EPA requirements which will regulate emissions for gas engines down to 50 hp, we felt that there was a need in the market for more effective control of small gas engines," said Rick Fisher, vice president of sales and marketing for Continental Controls. "We knew that we could apply the same techniques that we had applied to larger engines on these 40 to 300 hp engines, and it has proven to be very successful."
The EGC 2 is an air-fuel ratio system designed to combine several components into a single unit. It consists of a venturi mixer and an electronic pressure regulator that work together to provide precise control of the fuel-air ratio in response to an oxygen sensor located in the exhaust. The single unit mounts on the butterfly valve and directly replaces a conventional carburetor. By combining the fuel pressure regulator, mixing venturi and fuel control valve, the installation of the fuel system is greatly simplified and the design and performance for each component are optimized for controlling a precise fuel mix to small gas engines.
Not only does the EGC 2 eliminate the traditional mechanical carburetor and diaphragm and pressure regulator, eliminating a frequent maintenance issue, but it generally lowers the overall cost of the fuel system, the company said. The single unit also makes it possible to optimize the design for small gas engines.
The air entering the engine passes through the venturi mixer, its shape is designed to produce a low pressure at the throat of the venturi. This throat pressure is used to draw the fuel through the injection ports into the air stream. The size of the injection ports and the shape of the venturi are designed to work together to provide the stoichiometric mixture at all load and speed conditions. This eliminates the spring mass, diaphragm actuator and mixing bowl apparatus of typical mechanical carburetors.
The EGC 2 offers full authority fuel control, allowing control of a wide range of fuel types and heating values with a single carburetor. The unit can control gaseous fuels such as natural gas, propane, digester biogas and trash gas.
The key to the success of the EGC 2, according to Fisher, is in the patented variable pressure control technique used for control. This, along with the improved mixing from the venturi; the speed with which the fuel valve can react to changes in load or fuel heating value; and the electronic controls that offer "no droop," all contribute to what the company called the most sophisticated fuel control for small gas engines. The pressure setpoint is varied based on an input from a standard zirconium oxide 02 sensor located in the exhaust stream.
If the heating value of the fuel changes while the engine is running under the control of the 02 sensor control, the EGC 2 is designed to automatically adjust the injection pressure to maintain the mixture and the low emissions.
For application on the EGC 2, the fuel gas supply pressure should be between 1 psig and 5 psig at the carburetor gas inlet, which is the inlet to the electronic pressure regulator. A very precise pressure transducer is provided in the annulus surrounding the gas injection holes in the mixer. The pressure transducer measures the gas injection pressure. This signal is compared to a setpoint in the electronic system and a controller adjusts the pressure to match the setpoint.
The result is that when air flows through the mixer, a lower pressure is developed in the throat of the mixer which draws the correct amount of fuel into the air stream to provide the correct mixture for stoichiometric operation. The air-fuel mixture is then trimmed by adjusting the setpoint of the electronic pressure regulator based on the oxygen content in the exhaust.
The EGC 2 is designed to maintain the gas injection pressure near zero for all conditions, so load changes do not require a resetting of the pressure control. Therefore, the engine does not go out of compliance during a load transient, or if it does change, it will come right back in when the oxygen sensor feedback signal indicates the error, Continental Controls said.
The new carburetor requires a 10 to 32 Vdc minimum to maximum power source. The data from the carburetor is available digitally through a Modbus or CANBus serial link. By communicating all measured parameters and logged faults, the EGC 2 becomes integral to the complete engine system on-board diagnostic (OBD) solution. An optional display or laptop computer can also be used that will allow the user to monitor oxygen sensor output, gas injection pressure, and pre- and post-catalyst temperatures.
The unit is fully automatic and starts the engine with a default pressure setting. When the [O.sub.2] sensor is determined to be operating properly, it automatically will adjust the pressure setpoint to minimize the emissions. Data is available serially through Modbus for fuel pressure, [O.sub.2] sensor reading, [O.sub.2] sensor setpoint and gain setpoints.
The EGC 2 can be used with the Continental Controls display unit model ECVI to display the following data from the EGC 2: [O.sub.2] sensor output and its setpoint; gas injection pressure and its setpoint; default pressure setting and the pre- and post-catalyst temperatures. The ECVI provides a graphical representation of the variables and provides a means of adjusting the setpoints for the [O.sub.2] sensor and the default pressure, and other minor tunables and variables.
Continental Controls has units available for sale to OEMs, and packagers immediately and will be marketing complete end-user emissions reduction packages that will include turnkey kits with three-way catalysts and installation kits for the electronic carburetor in the near future.
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|Title Annotation:||ENGINE CONTROLS; introduction of EGC 2 carburetor|
|Publication:||Diesel Progress North American Edition|
|Date:||Nov 1, 2006|
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