WO1999046495A1

WO1999046495A1 - Method for ensuring delivery of at least a pilot quantity of liquid fuel in a dual fuel engine

Info

Publication number: WO1999046495A1
Application number: PCT/US1999/004477
Authority: WO
Inventors: Scott C. Brown; Martin L. Willi
Original assignee: Caterpillar Inc.
Priority date: 1998-03-11
Filing date: 1999-03-02
Publication date: 1999-09-16

Abstract

A method for ensuring delivery of a desired pilot quantity of liquid fuel in a dual fuel engine (12) wherein a value indicative of a determined liquid fuel energy rate for the engine (12) is determined and compared to a value, preferably predetermined, indicative of a liquid fuel energy rate for the desired liquid fuel pilot condition and, if the value indicative of the determined liquid fuel energy rate is less than the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition, then increasing a value indicative of an actual liquid fuel energy rate for the engine (12) to a level corresponding to the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition. The determined liquid fuel energy rate for the engine (12) can be based on a governor output, a fuel energy rate determination or computation for the engine (12), or other suitable determinant. The liquid fuel energy rate for the desired liquid fuel pilot condition can be based all or in part on factors including, but not limited to, operating parameters such as engine speed, fuel injection timing, load, and the like, as well as other factors such as fuel quality and the like. Preferably, values indicative of the liquid fuel energy rate, or the energy rate itself, for the desired liquid fuel pilot condition are determined through testing or other suitable means and stored in a memory device such as a lookup table or map associated with the engine control module or other engine control device.

Description

METHOD FOR ENSURING DELIVERY OF AT LEAST A PILOT QUANTITY OF LIQUID FUEL IN A DUAL FUEL ENGINE

Technical Field

This invention relates generally to dual fuel engines, and more particularly, to a method for ensuring delivery of at least a pilot quantity of liquid fuel to the engine during a dual fuel operating mode, particularly under changing engine speed and/or fuel injection timing conditions.

Background Art A dual fuel engine can typically operate in two modes. In a strictly liquid fuel mode a liquid fuel, such as diesel fuel, is injected directly into an engine cylinder or a precombustion chamber as the sole source of energy during combustion. In a dual fuel mode a gaseous fuel, such as natural gas, is mixed with air in an intake port of a cylinder and a small amount or pilot amount of the liquid fuel is injected into the cylinder or the precombustion chamber and ignited by compression in order to ignite the mixture of air and gaseous fuel.

Reference Smith, U.S. Patent No. 4,641,625, issued 10 February 1987; Durbin, U.S. Patent No. 5,140,959, issued 25 August 1992; and Beck U.S. Patent No. 5,450,829, issued 19 September 1995, which disclose various methods and apparatus for controlling fuel delivery in dual fuel engines.

A problem, that may be potentially damaging to the dual fuel engine, can occur when an unburned gaseous fuel passes through the engine. This can occur when an - 2 -

insufficient quantity of the liquid fuel is injected into the cylinder such that the mixture of air and gaseous fuel is either not ignited, or is incompletely combusted due to poor ignition. Conversely, if a greater amount of liquid fuel than that necessary for pilot purposes is injected into a engine cylinder, poor fuel economy and higher emissions of pollutants can result .

Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above .

Disclosure Of The Invention

In one aspect of the present invention a method for ensuring delivery of a desired pilot quantity of liquid fuel in a dual fuel engine is disclosed, the method including a first step of determining a value indicative of a determined liquid fuel energy rate for the engine, and a second step of comparing the value indicative of the determined liquid fuel energy rate to a value, preferably predetermined, indicative of a liquid fuel energy rate for a desired liquid fuel pilot condition and, if the value indicative of the determined liquid fuel energy rate is less than the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition, then increasing a value indicative of an actual liquid fuel energy rate for the engine to a level corresponding to the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition.

The desired liquid fuel pilot condition is preferably a condition wherein a minimum quantity of liquid fuel sufficient to cause ignition and substantially complete combustion of the gaseous fuel is - 3 -

delivered to the engine. This value and the other values indicative of liquid fuel energy rates used can be any suitable indicator of liquid fuel delivery to the engine, such as, but not limited to, a liquid fuel injector signal duration. The determined liquid fuel energy rate for the engine can be based on a governor output, a fuel energy rate determination or computation for the engine, or other suitable determinant, and the liquid fuel energy rate for the desired liquid fuel pilot condition can be based all or in part on factors including, but not limited to, operating parameters such as engine speed, fuel injection timing, load, and the like, as well as other factors such as fuel quality and the like. Because the liquid fuel energy rate for the desired liquid fuel pilot condition is based on factors that can vary, such as engine operating conditions including speed and the like, the liquid fuel energy rate for the desired pilot condition can likewise vary. Accordingly, values indicative of this energy rate for a wide range of conditions are preferably predetermined through testing or other suitable means and stored in a memory device such as a look-up table or map in an engine control module or elsewhere, so as to be retrieved by the engine control module or other device for controlling the engine for making the above comparison.

In operation in accordance with a preferred aspect of the present invention, the engine control module determines the liquid fuel injector control signal duration or other indicator of the determined liquid fuel energy rate from the governor, fuel energy rate computation or other source, and compares it to the retrieved liquid fuel injector control signal duration - 4 -

or other indicator for the liquid fuel energy rate for the desired pilot condition. If the determined injector control signal duration is less than the injector control signal duration for the desired pilot condition, then the engine control module will incorporate the injector control signal duration for the desired pilot condition into the liquid fuel injector signal which controls the quantity of liquid fuel delivered to the engine by the liquid fuel injector or injectors. If the determined fuel injector control signal duration is greater than the injector control signal duration for the desired pilot condition, then the engine control module will incorporate the determined fuel injector control signal duration into the liquid fuel injector signal.

Brief Description Of The Drawings

Fig. 1 is a schematic view of a dual fuel engine system in accordance with the present invention; and

Fig. 2 is a flowchart of operating steps for the dual fuel engine system of Fig. 1 in accordance with the present invention.

Best Mode For Carrying Out The Invention

Referring to the drawings, numeral 10 in Fig. 1 depicts a dual fuel engine system used in association with the present invention, including an internal combustion engine 12 having a representative cylinder 14. Although only one cylinder 14 is shown, it is recognized that the number of cylinders of engine 12 could vary and that engine 12 could be of the in-line type, V-type, or alternatively a rotary engine. A piston 16 is positioned for reciprocal movement in - 5 -

cylinder 14, which cylinder 14 is in communication with an intake port 18 and an exhaust port 20, which communication is controlled by respective valves 22 and 24. Intake port 18 receives air from an air intake manifold 26 to which intake air travels after passing through, for example, an air filter (not shown) . Engine 12 includes a fuel injector 28, such as an electronic unit injector, positioned for injecting liquid fuel, such as diesel fuel, into cylinder 14. The liquid fuel may be provided to fuel injector 28 by means commonly known in the art (not shown) . A gaseous fuel admission valve 30 is positioned between a gaseous fuel manifold 32 at an upstream side and intake port 18 at a downstream side, a nozzle portion of valve 30 extending into intake port 18 for delivering gaseous fuel thereto. Gaseous fuel admission valve 30 may, for example, be of the type shown and described in U.S. Patent No. 5,398,724 available from Woodward Governor Company. Gaseous fuel manifold 32 is connected to a source of gaseous fuel 34 by fuel path 36, a solenoid operated gaseous fuel shut off valve 38 being positioned along fuel path 36. Although not shown, it is recognized that such a system might typically include a balance regulator positioned between gaseous fuel source 34 and gaseous fuel manifold 32 for regulating the gaseous fuel pressure at the upstream side of gaseous fuel admission valve 30.

Dual fuel system 10 includes an electronic control module (ECM) 40 which is representative of a wide variety of engine control means including processor means, such as a microcontroller or microprocessor, as well as electronic circuitry, such as input/output circuitry, and associated memory. ECM 40 is connected to a pressure sensor 42 via conductive path 44 and to a - 6 -

pressure sensor 46 via conductive path 48 for receiving pressure indicative signals from each of such sensors. Such pressure sensors are well known in the art and therefore a detailed description of the sensors is not included herein. A temperature sensor 43 is also provided in gaseous fuel manifold 32 to provide temperature indicative signals to ECM 40 via conductive path 45. ECM 40 is connected for controlling gaseous fuel admission valve 30 by conductive path 50 and is also connected for controlling fuel injector 28 by conductive path 52. In this regard it is know to include driver circuitry within an ECM such as ECM 40 for delivering current control signals to such devices. However, it is recognized and contemplated that such driver circuitry could be formed separate from, but connected to, ECM 40. An engine speed sensor 54 associated with a crankshaft, camshaft or other indicator of the operating speed (not shown) of engine 12 is also connected to ECM 40 via conductive path 56 for delivering engine speed indicative signals thereto.

A mode switch 58 is connected to ECM 40 via conductive path 60 and is operable by an operator to select a liquid fuel operating mode or a dual fuel operating mode. The actual engine operating mode is determined based upon the mode switch selection and other monitored engine parameters .

ECM 40 further includes an associated governor 62 for processing selected of the above mentioned input signals and generating output signals for controlling a selected operating parameter or parameters of engine 12, such as engine speed, either solely or in association with operator input . Governor 62 can be operable to control the selected parameter or parameters such as engine speed in a suitable manner such as by controlling - 7 -

a liquid fuel energy rate, gaseous fuel energy rate, and/or total fuel energy rate, delivered to engine 12. For example, if engine 12 is to be operated in the liquid fuel mode, governor 62 is operable to generate an output signal having a value which is indicative of a liquid fuel rate necessary to maintain a desired engine speed based upon a comparison of the actual engine speed and the desired engine speed. The desired engine speed may be a predetermined engine speed stored in a suitable memory device such as internal memory 64 shown, or it may be indicated by an operator input such as a throttle setting, for example. Because engine 12 is to be operated in the liquid fuel mode, in this instance the liquid fuel energy rate is also indicative of the total fuel energy rate for maintaining the desired engine speed. From the liquid fuel energy rate the duration of a fuel injector control signal for the desired engine speed can be determined. Liquid fuel is then caused to be delivered to engine 12 by delivering a control signal of the determined duration to fuel injector 28.

As another example, if engine 12 is to be operated in the dual fuel mode, governor 62 is operable to produce an output signal value indicative of a desired total fuel energy rate to maintain the desired engine speed. A first value indicative of the desired liquid fuel rate and a second value indicative of the desired gaseous fuel energy rate can then be determined in a suitable manner, and a duration of a gaseous fuel admission valve control signal necessary to inject gaseous fuel in amount which provides the desired gaseous fuel energy rate can be determined and the duration of a fuel injector control signal necessary to inject liquid fuel in an amount which provides the desired liquid fuel rate can be determined. The gaseous - 8 -

fuel and liquid fuel are then caused to be delivered to engine 12 under control of control signals incorporating the determined durations sent to valve 30 and injector 28. In the liquid fuel mode the liquid fuel is injected into engine cylinder 14 via injector 28 and serves as the sole source of fuel energy for combustion. In the dual fuel mode the gaseous fuel is mixed with air in intake port 18 and inducted into cylinder 14, and the liquid fuel is injected into cylinder 14 where it is ignited by compression to thereby combust and ignite the mixture of air and gaseous fuel. Generally, in the dual fuel mode it is desirable to limit the amount of liquid fuel injected to a pilot quantity sufficient to ignite the mixture of air and gaseous fuel, so as to minimize liquid fuel costs, as well as emissions of unburned liquid fuel and pollutants from combustion of the liquid fuel. However, and importantly, if less than a pilot quantity of liquid fuel is injected into the cylinder, the mixture of air and gaseous fuel may not be sufficiently ignited or may incompletely combust, which can result in poor engine performance, emissions problems, and possible engine damage. Accordingly, when in the dual fuel mode, dual fuel system 10 is desirably operable to ensure delivery of a desired pilot quantity of liquid fuel to engine 12, preferably an amount corresponding to a minimum liquid fuel energy rate sufficient to provide complete combustion of the air and gaseous fuel mixture, yet not so great as to produce undesirable levels of emissions of pollutants.

Referring to Fig. 2, a high level flow chart 66 of operating steps in accordance with the present invention for ensuring delivery of the desired minimum pilot quantity of liquid fuel to engine 12 while - 9 -

operating in the dual fuel mode is shown. At a first step 68 a value indicative of a determined liquid fuel energy rate for engine 12 is determined. This value is preferably a liquid fuel injector control signal duration. At a step 70 the value indicative of the determined liquid fuel energy rate from step 68 is compared to a value, preferably predetermined and retrieved from memory 64 (Fig. 1), indicative of a liquid fuel energy rate for the desired liquid fuel pilot condition, and which is also preferably a liquid fuel injector control signal duration. If the value indicative of the determined liquid fuel energy rate is the lesser value, then in a step 72 a value indicative of an actual liquid fuel energy rate for the engine (also preferably a liquid fuel injector control signal duration) is increased to a level corresponding to the predetermined value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition by ECM 40. Conversely, if the value indicative of the determined liquid fuel energy rate from step 68 is greater than the value indicative of a liquid fuel energy rate for the desired liquid fuel pilot condition, then the value indicative of an actual liquid fuel energy rate for the engine can optionally be set at a level corresponding to the determined value indicative of the determined liquid fuel energy rate or some other value (not shown) .

The determined liquid fuel energy rate for the engine can be based on a governor output, a total or other fuel energy rate computation for the engine, or any other suitable determinant, and the liquid fuel energy rate for the desired liquid fuel pilot condition can be based all or in part on factors including, but not limited to, operating parameters such as engine - 10 -

speed, fuel injection timing, load, and the like, as well as other factors such as fuel quality and the like, engine speed and timing being the preferred factors. Since the preferred factors (engine speed and timing) are expected to vary, the liquid fuel energy rate for the desired liquid fuel pilot condition will also vary, and predetermined liquid fuel energy rates for a wide range of contemplated engine operating conditions are preferably determined by testing or other suitable means and stored in a memory device such as memory 64, a map file such as a 3 -dimensional map file, or the like, for retrieval by ECM 40 in step 70.

Here, it should be recognized that the steps of Fig. 2 above can be performed for engine 12 on an overall basis, or, individually for each cylinder of the engine, as desired.

Industrial Applicability

The present invention provides a method for ensuring the delivery of a minimum desired pilot quantity of liquid fuel to an engine operating in a dual fuel mode wherein, for instance, a mixture of air and a gaseous fuel such as natural gas or methane is ignited by the liquid fuel which can be diesel fuel, other oil based fuels, and the like. The present invention has applicability for use with a wide variety of dual fuel engines, including engines used in applications such as stationary applications for pumping, generation of electricity, and other purposes, as well as a wide variety of vehicular applications. Additionally, although it is disclosed herein to ensure the delivery of the desired quantity of liquid fuel based on parameters including engine speed and timing, it is likewise contemplated that such fuel quantity could be - 11 -

based on other parameters in addition to, or instead of, those. Similarly, the present method has applicability for use with dual fuel engines controlled by means other than the herein described governor. Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

- 12 -Claims

1. A method for ensuring delivery of at least a desired pilot quantity of liquid fuel to a dual fuel engine (12), said method comprising the steps of: a) determining a value indicative of a determined liquid fuel energy rate for the engine (12); and b) comparing the value indicative of the determined liquid fuel energy rate determined in step a) to a value indicative of a liquid fuel energy rate for a desired liquid fuel pilot condition and, if the ╬¢^alue indicative of the determined liquid fuel energy rate is less than the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition, then increasing a value indicative of an actual liquid fuel energy rate for the engine (12) to a level corresponding to the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition.

2. The method, as set forth in claim 1, wherein the value indicative of the actual liquid fuel energy rate for the engine (12) is a liquid fuel injector control signal duration for the engine (12) .

3. The method, as set forth in claim 1, wherein the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition is a predetermined liquid fuel injector control signal duration required to inject a corresponding pilot quantity of liquid fuel into a combustion cylinder (14) of the engine (12) . - 13 -

4. The method, as set forth in claim 3, wherein the predetermined liquid fuel injector control signal duration is determined at least in part based on a timing condition of the engine (12) .

5. The method, as set forth in claim 3, wherein the predetermined liquid fuel injector control signal duration is determined at least in part based on a speed condition of the engine (12) .

6. The method, as set forth in claim 1, where in step b) the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition is a predetermined value retrieved from a look-up table (64) .

7. The method, as set forth in claim 1, wherein the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition is determined at least in part by an engine governor (62) .

8. The method, as set forth in claim 1, wherein the value indicative of the liquid fuel energy rate for the desired liquid fuel pilot condition is determined at least in part based on a total energy rate determination for the engine (12) .

9. The method, as set forth in claim 1, wherein the liquid fuel is a diesel fuel.

10. A method for ensuring injection of at least a desired pilot quantity of liquid fuel into a combustion chamber of a dual fuel engine (12) , said method comprising the steps of: - 14 -

a) determining a liquid fuel injector control signal duration for liquid fuel injected into the combustion chamber (14) ; and b) comparing the liquid fuel injector control signal duration determined in step a) to a predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel and, if the liquid fuel injector control signal duration determined in step a) is less than the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel, then producing a liquid fuel injector signal for the combustion chamber (14) incorporating the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel.

11. The method, as set forth in claim 10, where in step b) if the liquid fuel injector control signal duration determined in step a) is greater than the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel, then producing a liquid fuel injector signal for the combustion chamber 914) incorporating the liquid fuel injector control signal duration determined in step a) .

12. The method, as set forth in claim 10, where in step a) the liquid fuel injector control signal duration is determined at least in part by an engine governor (62) .

13. The method, as set forth in claim 10, where in step a) the liquid fuel injector control signal - 15 -

duration is determined at least in part based on a total energy rate computation for a desired combustion condition in the combustion chamber (14) .

14. The method, as set forth in claim 10, wherein the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel corresponds to a liquid fuel energy rate computation for a desired combustion condition in the combustion chamber (14) .

15. The method, as set forth in claim 10, wherein the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel is retrieved from a look-up table (64) .

16. The method, as set forth in claim 10, wherein the predetermined minimum liquid fuel injector control signal duration for the desired pilot quantity of liquid fuel is determined based at least in part on an engine speed parameter and in part on a liquid fuel injection timing parameter.

17. The method, as set forth in claim 10, wherein the liquid fuel is a diesel fuel.