Patent Application
20130220274
The present disclosure relates to the field of control systems for engines. In particular, the present disclosure relates to the field of control systems for dual fuel engines.
In diesel-electric multiple units (DEMU), a diesel engine drives an electrical generator which produces electrical energy. A dual fuel engine is an engine integrated with an additional system allowing utilization of gaseous fuel, typically natural gas, as a supplemental fuel by using a certain level of liquid fuel (Pilot Fuel) for operation and for ignition of the gaseous fuel. The generated power is then fed to electric traction motors for driving wheels of a locomotive. The Diesel Electric Multiple Units (DEMU), typically operate in eight notches (steps). Every notch is characterized by a pre-determined speed and load. Hence the governor of the locomotive needs to control both the engine speed and the generator load. For diesel operation, the engine control is entirely achieved with the Diesel Actuator and is therefore a simple control. However, for dual fuel operation, a control strategy for introducing gas with proper control and limiting diesel needs to be developed. The dual fuel engine has a number of quality attributes. A primary benefit of using dual fuel engine is that it provides fuel flexibility, cleaner operation, use of cheaper natural gas when available and can operate on liquid fuel alone when necessary.
The presently available dual-fuel engine is integrated with a standard diesel engine. A measured quantity of natural gas is mixed with the air just before it enters the cylinder and compressed to the same levels as the diesel engine to maintain efficiency. The natural gas mixture does not ignite spontaneously under compression. Hence a small amount of diesel fuel is injected. The amount of diesel fuel injected acts like a multitude of microscopic spark-plugs, setting off clean and efficient combustion of the lean gas-air mixture.
Thus, there was felt a need for a control system that enables overcoming of the drawbacks of dual fuel engines known in the art.
This disclosure provides a method of optimized fuel induction at a particular revolution per minute (RPM) of an engine for dual fuel operation in an engine adapted to be operated using a liquid fuel and a gaseous fuel at varying loads and engine speeds, the method comprising: inducting the gaseous fuel and the liquid fuel into the engine commencing from a predetermined lower engine load limit; increasing an amount of gaseous fuel inducted into the engine as the engine load increases from the predetermined lower engine load limit to a predetermined upper engine load limit; limiting an increase in the amount of gaseous fuel inducted into the engine at engine load levels above the predetermined upper engine load limit; and increasing the amount of liquid fuel inducted by a predetermined quantity at engine load levels above said predetermined upper engine load limit.
Typically, in accordance with the present disclosure, the method of optimized fuel induction comprising:
Typically, in accordance with the present disclosure, the predetermined lower limit is in the range of 20 to 25% load.
Typically, in accordance with the present disclosure, the method of optimized fuel induction further comprising actuating a liquid fuel actuator and maintaining a gaseous fuel actuator in a closed position prior to the predetermined lower limit.
Preferably, in accordance with this disclosure, co-feeding gaseous fuel further comprises controlling a liquid fuel actuator to induct controlled liquid fuel and controlling a gaseous fuel actuator to induct gaseous increasingly.
Typically, in accordance with the present disclosure, the method of optimized fuel induction further comprises actuating a liquid fuel actuator for boosting the liquid fuel induction by a pre-determined quantity beyond the predetermined upper limit and maintaining the gaseous fuel actuator within a maximum specified limit.
In accordance with the present disclosure, there is provided a control system for optimized fuel induction for dual fuel operation in an engine adapted to be operated by a liquid fuel and a gaseous fuel at varying loads and engine speeds,
the system comprising:
The system and method of the present disclosure will now be explained in relation to the accompanying drawings, in which:
Control systems for dual fuel engines using field retrofit kits consisting of Programmable Logic Controller (PLC) and gas valves are known in the art. However, Applicant has recognized that the presently available dual fuel engines, including those using retrofit kits, are not capable of providing precise control for injection of diesel and gas under all operating conditions often resulting in emission problems.
The control of substitution of fuel with gas is indirect in the known prior art system 100. When dual fuel operation is initiated, the PLC gradually opens the Gas Actuator thereby inducting gas into the intake air stream. This reduces the diesel requirement. Gas is admitted until the diesel fuel pressure reduces to a desired value. Closed loop Speed control is achieved using a Diesel Actuator. During transient conditions, the Diesel Actuator takes over since the response of Diesel is faster, thus leading to over fueling, until stable operation with Gas Actuator is achieved.
Furthermore, the load feedback in the system 100 is also indirect. The excitation logic takes load feedback based on Diesel Actuator current. Gas substitution reduces the Diesel Actuator current and needs to be manipulated for load feedback requirement. This impacts the stability and accuracy of the excitation control of the generator.
Thus engine operation using control systems as illustrated in
Several attempts have been made to provide reliable control systems for dual fuel engines. For instance, U.S. Pat. No. 6,543,395 discloses a bi-fuel control system for diesel engines and employs indirect control of the substitution of gas resulting in drawbacks explained herein above. It also involves complex calculations to decide the amount of gas for opening the gas valve precisely. Furthermore, U.S. Pat. No. 6,101,986 discloses a method for a controlled transition between operating modes of a dual fuel engine, wherein complex energy calculations are involved to decide the amount of fuel and gas to be delivered. Therefore, the aforesaid attempts towards providing a stable and reliable control system for dual fuel engines lack simplicity besides being unable to provide adequate control of the substitution needs of a dual fuel engine.
Therefore, in accordance with the present disclosure, a control system for dual fuel engines is envisaged that provides the following functions:
Dual fuel engines with a control system in accordance with the present disclosure provide closed loop control for limiting the quantity of diesel fuel consumed during the dual fuel operation. Initially, up to about 25% load, the engine operation is based on liquid fuel only and then dual fuel operation starts and gaseous fuel is inducted along with the liquid fuel. The speed control is transferred to a Gas Actuator in the dual fuel mode. Above a certain load, gaseous fuel cannot be increased, hence the amount of liquid fuel is increased, still limiting it in the closed loop. The liquid fuel used is typically diesel while the gaseous fuel used is natural gas.
The present disclosure will now be described with reference to an exemplary embodiment shown in the accompanying drawings. The embodiment does not limit the scope and ambit of the inventions. The description relates purely to the exemplary preferred embodiment and its suggested applications.
A typical locomotive operates in 8 notches (steps). Every notch is characterized by a pre-determined speed and load. Hence, the governor of the locomotive needs to control both the engine speed and the generator load. For liquid fuel mode operation, the speed control of the engine (210) is entirely handled by a liquid fuel actuator and hence is a simple control. Speed control during liquid fuel mode of operation is represented by a block (216) and involves control of the fuel Actuator using speed as an input for the control logic. Block (218) represents Load KW control during liquid fuel mode of operation and involves control of the excitation of the generator (212) using load as an input for the control logic. For dual fuel operation, the control strategy for introducing gas and limiting liquid fuel is complex and needs to be optimized. Block (220) represents speed control during dual fuel operation and involves liquid fuel control, substitution control and Gas Actuator control using speed as an input for the control logic. Block (222) represents Load KW control (using Potential Transformer/Current Transformer modules for KW feedback) during dual fuel operation and involves control of the excitation of the generator (212) using load as an input for the control logic.
The governor (410) provides an output signal to a liquid fuel actuator (468), a gas actuator (474), a gas solenoid valve (472), a liquid fuel solenoid valve (470), a fault code lamp (464) and an excitation hardware module (420). The liquid fuel actuator (468) and the gas actuator (474) enable controlling the speed of operation of the engine in the liquid fuel mode and the dual fuel mode respectively. The liquid fuel shutoff valve (470) enables in turning off the engine while the gas shutoff valve (472) enables turning off the supply of gas in case of emergency. The liquid fuel shutoff valve (470) and the gas shutoff valve (472) are typically solenoid valves. The fault code lamp (464) enables providing indication of any operation fault or any fault in the sensors. The excitation hardware module (420) enables amplifying the 24 volts power supply to the governor (410) from the battery (416) to 110 volts DC. The amplified power of 110 volts is supplied to field windings of a traction generator (422) to produce a voltage and current through the potential transformer (424) and the current transformer (426).
The open loop performance of the dual fuel engine in the dual fuel mode is carried out by firstly determining a lower limit below which only the liquid fuel is inducted in to the engine, represented by D in
In the dual fuel mode, represented by DF, the maximum amount of liquid fuel and the maximum amount of gaseous fuel to be inducted is determined by considering the thermal limits of the engine namely Turbine Inlet Temperature (TIT), Turbine Outlet Temperature (TOT) and Peak combustion Temperature, Mechanical limits namely Peak Cylinder Pressure, Knock Margin and Exhaust Emissions namely NOx, THC, CO and Smoke.
The open loop optimization logic provides the following values that are then used in the closed loop substitution logic in order to overcome the performance issues that were noticed:
The optimization of the lower limit and the upper limit is carried out by maintaining the total energy produced during dual fuel mode of operation of the engine equal to the total energy in obtained in the liquid fuel mode. During optimization of the lower limit and the upper limit, optimized values for fuel rail pressure, gaseous fuel throttle position, exhaust gas temperature and intake manifold temperature are recorded and are used as inputs to the substitution logic, shown in
Initially, the speed control is achieved with Liquid Actuator (468) PID (proportional-integral-derivative) control and the Gaseous fuel Actuator (474) is maintained in closed position.
When the lower limit is reached, as identified by manifold pressure MAP_SP1 and Liquid Fuel Pressure FRP_SP1, the speed control is transferred to the Gaseous fuel Actuator (474) PID control while the Liquid Actuator (468) is in the Load Limit mode DA-LLM by fuel pressure feedback and hence the induction of liquid fuel quantity is limited. This is a closed loop PID control with Fuel Rail Pressure as a feedback.
As the load further increases, which is identified by the intake manifold temperature and pressure, the Load limiting Set points for Liquid Fuel pressure DA-FP are incremented. For instance, at manifold pressure MAP_SP2, the fuel pressure DA-FP is increased to FRP_SP2 and similarly at MAP_SP3, the fuel pressure DA-FP is set to FRP_SP3. As the total energy produced during liquid fuel mode and dual fuel mode is required to be maintained constant at a predetermined load, the induction of the liquid fuel is boosted by a predetermined quantity so that amount of gaseous fuel induction does not exceed safe limits as determined by exhaust temperatures and knock levels.
The settable threshold parameters for achieving desired substitution and actions related to these thresholds are summarized as follows:
FRP_SP1: Fuel Rail Pressure limit for initial substation. Liquid Actuator (474) controls the engine speed up to this point. The Intake Manifold pressure at this point is MAP_SP1.
MAP_SP2: As the engine load increases and the Manifold pressure crosses MAP_SP2, the Fuel Rail Pressure is increased to FRP_SP2.
MAP_SP3: As the engine Manifold pressure crosses MAP_SP3, Fuel Rail pressure is increased to FRP_SP3.
GAS_POS_MAX: When Gaseous fuel Actuator (468) reaches this value for a particular RPM, the Gaseous fuel Actuator (468) is stopped from opening further.
The substitution logic of the control system for dual fuel engines provides the following features:
Thus, the Direct Multipoint Closed Loop Substitution Logic, shown in
Although the explanation provided herein above is with reference to a Diesel Electric Multiple Unit (DEMU), the control system for dual fuel engines in accordance with the present disclosure can be extended to other applications, for instance, gensets.
The technical advancements offered by the control system for dual fuel engines in accordance with the present disclosure which add to the economic significance include the realization of:
The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the inventions and the claims unless there is a statement in the specification to the contrary.
Wherever a range of values is specified, a value up to 10% below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the inventions.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the inventions. These and other changes in the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the inventions and not as a limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1677/MUM/2010 | Jun 2010 | IN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/38153 | 5/26/2011 | WO | 00 | 1/2/2013 |
