BI-FUEL CONVERSION SYSTEM
TECHNICAL OVERVIEW
The Bi-Fuel Conversion System allows conventional, reciprocating diesel engines to be operated utilizing a mixture of natural gas and diesel fuel. The Bi-Fuel Conversion System (BFCS) has been designed to allow diesel engines to operate on a mixture of natural gas (gas) and diesel fuel, with gas percentages typically ranging from 40% to 90% of total fuel consumed. The BFCS allows users to adjust gas-diesel fuel mixtures according to the specific requirements of the converted engine. The System has been designed to work with all grades of diesel fuel (#1, #2, #3 and heavy/bunker fuel) and with all methane gas types (including natural gas, bio-gas, well-head gas, etc.). Primary to the design of the BFCS is the ability of the engine to be automatically returned to 100% diesel operation in the event of any of the following fault conditions:
The engine may also be returned to 100% diesel operation manually by the operator. This is accomplished by a master Bi-Fuel on/off switch located on the BFCS main control panel. The BFCS has been designed so that in the event of either automatic or manual switching from Bi-Fuel mode to 100% diesel operation (and vice-versa), engine power output and stability is not interrupted.
The primary components of the BFCS are:
The BFCS consists of three major sub-systems:
Each of these three sub-systems are integrated such that their function relative to each other is seamless. The following is a description of each sub-system's operational details:
Gas Control Sub-System
The gas control sub-system (GCS) has been designed as a means of controlling the amount of gas supplied to the engine while operating in Bi-Fuel mode.
The GCS has been designed to allow the engine to utilize methane gas types with a supply pressure of between 1 and 5 p.s.i. The GCS design is "scaleable" so that it can be adapted to various size engines requiring differing gas flow rates. This includes engines with multiple turbochargers and/or superchargers and multiple air intakes. The GCS consists of a manual shut-off valve connected to supply gas at 1-5 p.s.i. The manual shut-off valve is included in the system for safety purposes as a positive control device which allows all gas flow to the BFCS to be stopped in the case of an emergency (gas leak, fire, etc.).
Downstream of the manual shut-off valve, a gas pressure sensor is installed which allows the BFCS to automatically switch to 100% diesel mode in the event that gas pressure drops below a specified set-point, or alternately, exceeds a maximum pressure value.
Downstream of the pressure sensor is located an electrically operated solenoid valve which provides a means for the BFCS to automatically stop gas flow to the engine in the event of either manual shut-down of the BFCS, automatic shutdown of the BFCS, or in the case of a shut-down of the engine. This design has been adopted in order to insure that positive pressure gas flow is stopped prior to reaching the gas regulating valve, which thus prevents gas flow into the engine at those times when it is not required.
Located downstream of the gas solenoid valve is the gas pressure regulator. The gas pressure regulator is a zero-governor, demand type regulator. The regulator reduces the inlet gas pressure (1-5 p.s.i.) to atmospheric pressure, whereby vacuum is required at the regulator outlet in order for gas to flow downstream from the gas regulator to the engine. This design has been adopted to allow the BFCS to utilize a "demand" gas control scheme whereby engine vacuum and intake airflow is utilized to determine gas flow requirements of the engine. As engine load increases, there is a corresponding increase in engine intake air volume and vacuum, and this vacuum is communicated to the gas pressure regulator which adjusts gas flow according to the strength of the vacuum signal generated by the engine (light load -low vacuum =low gas flow / high load =high vacuum =high gas flow).
Located downstream of the gas regulator is the gas control valve. The gas control valve is a butterfly type valve which is one of the adjustable components of the BFCS, and is set during the tune-in phase of the engine conversion. The gas control valve is an electrically operated valve which can be either fully open (de-energized state) or partially open (energized state). The "partially open" position of the gas control valve is adjustable to allow the BFCS to have a separate gas flow adjustment for light to medium engine load levels, and makes the BFCS more flexible for installation on engines which operate over a wide spectrum of load levels. The gas control valve is scheduled via the BFCS main control panel by monitoring engine MAP levels as determined by a sensor and control module. As engine load level increases to the medium to high level range, the gas control valve is commanded to open fully and no longer restricts gas flow to the engine.
Located downstream of the gas control valve is the gas power valve. The gas power valve is a needle type valve which is one of the adjustable components of the BFCS, and is set during the tune-in phase of the engine conversion. The power valve is used to set the maximum gas flow rate to the engine and once set, remains in a fixed position regardless of engine load. The power valve is the primary adjustment for setting gas flow levels at the medium to high load levels and acts as a safety device by restricting gas flow to a pre-determined maximum flow rate. Once the power valve is set, engine power output in Bi-Fuel mode is limited by this adjustment.
Located downstream of the gas power valve is the air-fuel mixing device. The mixer is of a fixed venturi design and is installed upstream of the engine air-intake, such that all of the incoming air is directed through the mixer. In the case of engines with multiple air-intake systems, one mixer is used for each of the intakes. The BFCS has been designed to utilize mixing devices which do not incorporate any type of air throttle plate in their design. By utilizing a "demand" regulator and a "fixed venturi" type mixer, the BFCS insures that the basic engine operating efficiency will not be negatively impacted by use of the System.
Conventional diesel engines do not utilize an air-throttle device thereby avoiding "pumping losses" which incur significant efficiency penalties. Similarly, the BFCS does not utilize a throttle plate in it's design and thereby maintains an efficiency level during Bi-Fuel operation comparable to 100% diesel operation. After exiting the mixing device, the air-gas mixture is then ingested into the engine air-intake manifold system where it is then distributed to each intake valve as per the normal intake air distribution scheme of the engine. As each intake valve opens as per the valve timing scheme of the engine, the air-gas mixture is delivered to the cylinder for combustion.
Diesel Control Sub-System
The diesel control sub-system (DCS) has been designed as a means of controlling the amount of diesel fuel supplied to the engine while operating in Bi-Fuel mode. The DCS utilizes either a Diesel Fuel Control Valve (DFCV), or alternately, a solenoid operated rack actuator. In either case, the role of the DCS is to limit the total possible diesel fuel flow thereby allowing for the substitution of natural gas.
The primary component of the DCS is the diesel fuel control valve (DFCV) which is installed in the fuel system of the generator. The DFCV is an electrically operated 3-way valve (12VDC or 24VDC) which incorporates an internal needle valve assembly. The DFCV can be manually adjusted such that when in the energized state, the flow of diesel fuel through the valve is significantly restricted, thereby effectively decreasing the quantity of diesel fuel supplied to the engine and allowing for substitution of the above described air-gas mixture during Bi-Fuel operation. For engines with duty cycles that include wide variations in load, an alternative DFCV device may be used which employs a secondary internal needle valve assembly. This allows for fine adjustment of diesel fuel flow in both the light to medium and medium to heavy load ranges. In this case, the DFCV is scheduled via the BFCS main control panel by monitoring engine MAP.
Installation of the DFCV will vary according to the fuel delivery system design of the engine. Typically, two types of fuel delivery systems are employed; (1) rail type systems which supply fuel to rocker-arm activated diesel injectors via a fuel galley under relatively low pressure and (2) positive displacement systems which activate each injector with high pressure diesel fuel from a distributor type pump. In the case of the fuel rail type systems, the DFCV is installed between the pump supplying fuel to the fuel rail and the rail inlet orifice (see figure 2). In the case of distributor pump type fuel systems, the DFCV is installed directly upstream of the injection pump fuel inlet orifice (see figure 3).
When in the de-energized state, the DFCV restores full diesel fuel flow capacity by diverting the fuel path around the internal needle valve cartridge, thereby allowing the engine to operate in 100% diesel fuel mode. Additionally, the DFCV assembly includes a means for relieving fuel back pressure which results on the inlet side of the valve as a result of the needle valve restriction. As fuel pressure increases past approximately 60 p.s.i., a one-way check valve with a cracking pressure of 60 p.s.i, allows diesel fuel to flow to the diesel fuel return system thereby relieving potentially harmful fuel back pressure.
Note: See addendum for description of rack-actuator installation and operation.
The Electronic Control and Monitoring Sub-System (ECMS) has been designed as a means of controlling various components of the BFCS and also provides a means to monitor critical engine and system parameters and display faults and system status to the user locally and/or remotely. The ECMS has a general fault indicator light and an alpha-numeric LCD display to notify the user of the type of fault and the time which it occurred. All faults except low engine MAP are 'latching" faults which require the operator to reset the ECMS before Bi-Fuel operation will resume. In addition, the ECMS can "call-out" via land line or serial port to notify the user of a fault condition.
The ECMS is powered from the engine panel or starting batteries with 24 VDC. Current flows to the ECMS through the OEM oil pressure safety system. If the engine loses oil pressure, the ECMS will deactivate Bi-Fuel operation. The ECMS provides source power to the various components of the Bi-Fuel System and also monitors the following parameters:
Engine Exhaust Gas Temperature:
The ECMS includes a means for monitoring and displaying engine exhaust gas temperature (EGT). In the case of engines with dual exhaust systems (such as v-configured engines), each exhaust system can be independently monitored. EGT is displayed on the ECMS main panel via digital display. In the event that EGT (for either channel) exceeds a user programmed set-point, the ECMS will automatically shut-down the BFCS, return the generator to 100% diesel operation and notify the user via a panel mount LCD. Additionally, the ECMS will not re-start Bi-Fuel operation until the EGT fault has been reset by the operator.
Natural Gas Pressure:
The ECMS monitors natural gas input pressure to the Bi-Fuel System via a pressure transducer. The ECMS is field programmed to allow for a "window" of acceptable gas pressure. In the event that the gas pressure should drop below or rise above the programmed set-points, the ECMS will automatically shut-down the BFCS, return the generator to 100% diesel operation and notify the user via a panel mount LCD. Additionally, the ECMS will not re-start Bi-Fuel operation until the gas pressure fault has been reset by the operator.
Manifold Air Pressure:
The ECMS monitors engine MAP via a pressure transducer. This pressure data allows the user to set two (2) MAP set-points. The first set-point determines the "light-load" Bi-Fuel cut-off point. At engine loads below this level, the ECMS will deactivate the Bi-Fuel System and return the engine to 100% diesel fuel. The second set-point determines the maximum allowable engine MAP during Bi-Fuel operation. The operator can program the ECMS to limit the maximum allowable engine power in Bi-Fuel mode. If engine load exceeds this programmed limit, the ECMS will automatically shut-down the BFCS, return the generator to 100% diesel operation and notify the user via a panel mount LCD. Again, the ECMS will not re-start Bi-Fuel operation until the MAP fault has been reset by the operator.
The BFCS also incorporates a master "on-delay" time relay which is utilized with engines used as generator drives in paralleling operations. In the event that the generator is required to parallel with either another generator or the electric utility grid, the BFCS will delay initiating Bi-Fuel mode until such time as the generator has completed the paralleling operation on 100% diesel fuel. This "delay-on" function is field-adjustable and gives the user from 1 to 300 seconds to complete the paralleling operation before Bi-Fuel mode is initiated.