Internal-combustion engines – Combustion chamber means having fuel injection only – Using multiple injectors or injections
Reexamination Certificate
1998-03-06
2001-09-18
Kwon, John (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Using multiple injectors or injections
C123S300000
Reexamination Certificate
active
06289871
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to dual fuel engines and, more particularly, to a method for minimizing the delivery of liquid pilot fuel to each cylinder of a dual fuel engine during a dual fuel operating mode. The present method involves adjusting the liquid pilot fuel quantity to each cylinder based upon an analysis of the exhaust port temperature or other cylinder performance parameters associated with each individual cylinder.
BACKGROUND ART
A dual fuel engine can typically operate in two modes, namely, a dual fuel mode (gaseous fuel and liquid fuel) and a liquid fuel mode. 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 fuel and energy during combustion. In a dual fuel mode, a gaseous fuel, such as natural gas, is controllably released into an air intake port of the particular cylinder where the gaseous fuel is mixed with air. After a predetermined period of time, a small amount or pilot amount of diesel fuel is injected directly into the cylinder or precombustion chamber in order to ignite the mixture of air and gaseous fuel. Compression of the air/fuel mixture during the compression stroke ignites the liquid fuel which in turn ignites the air/gaseous fuel mixture.
The amount of minimum liquid pilot fuel necessary for delivery to each individual cylinder to assure good combustion may or may not be the same for each such cylinder due to differences in the operating characteristics of the fuel injectors and valves used to control liquid fuel delivery to such cylinder. Assuming the amount of minimum liquid pilot fuel necessary for delivery to each individual cylinder will be substantially the same for each such cylinder, due to variations in the operating characteristics of the liquid fuel injectors, each liquid fuel injector may require a somewhat different current pulse time in order to achieve the same fuel delivery to each respective cylinder. If the control signals used to deliver fuel to different cylinders are of the same duration, such variations can result in different amounts of liquid fuel being delivered to different cylinders. In addition, because the amount of liquid pilot fuel being delivered to a dual fuel engine is generally small compared to the amount of gaseous fuel being delivered to such engine during a dual fuel operating mode, any variation in the amount of liquid pilot fuel being delivered to the respective cylinders will be magnified and this could seriously effect optimal ignition and combustion of the air/gaseous fuel mixture within each such cylinder.
On the other hand, if the amount of minimum liquid pilot fuel necessary for delivery to each individual cylinder is, in fact, different, the combustion performance of each such cylinder must be evaluated in order to separately determine the least amount of liquid pilot fuel necessary to achieve optimal combustion performance in each respective cylinder. If too little liquid pilot fuel is utilized, optimum ignition and combustion will not be achieved and ignition within any particular cylinder may occur at a retarded timing, or such cylinder may misfire due to incomplete ignition of the gaseous fuel. In either case, deteriorated cylinder performance occurs.
It is therefore desirable to both determine the least amount of liquid pilot fuel necessary to achieve optimal ignition and combustion of the air/gaseous fuel mixture within each particular cylinder of a dual fuel engine for any particular engine operating condition, and thereafter deliver the corresponding minimal amount of liquid pilot fuel to each such cylinder. It is also desirable to minimize fuel cost and reduce the emissions associated with a dual fuel engine.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
Disclosure of the Invention
In accordance with the teachings of the present invention, a method for controlling and adjusting the delivery of liquid pilot fuel to each individual cylinder in a dual fuel engine using the exhaust port temperature of each such cylinder as a controlling parameter is provided. Before the delivery of liquid pilot fuel to any particular cylinder is adjusted in accordance with the present invention, it is preferred, although not required, that the delivery of gaseous fuel to that particular cylinder be balanced. This is accomplished by trimming all of the gaseous fuel admission valves associated with the dual fuel engine to a predetermined desired exhaust port temperature. This trimming will establish a substantially balanced delivery of gaseous fuel to each respective cylinder based upon the selected desired exhaust port temperature.
Trimming of the gaseous fuel admission valves involves operating the dual fuel engine in its dual fuel mode with a predetermined amount of liquid pilot fuel being delivered to each respective cylinder and thereafter sensing the actual exhaust port temperature of the particular cylinder under investigation. This actual exhaust port temperature is then compared to a predetermined desired exhaust port temperature and, based upon this temperature comparison, a trim value for that particular cylinder is generated. This trim value is indicative of a percentage (%) adjustment factor which is applied to the gaseous fuel admission valve control signal duration time for such cylinder. This, in effect, changes the gaseous fuel admission valve control signal duration time so as to control the gaseous fuel flow to that particular cylinder. Controlling the delivery of gaseous fuel individually to each cylinder likewise controls the air/gaseous fuel mixture for that particular cylinder and balancing the exhaust port temperature for each such cylinder to a common desired exhaust port temperature likewise corresponds to a balanced air/gaseous fuel ratio in all cylinders.
Once the gaseous fuel admission valves are trimmed to achieve a common desired exhaust port temperature as explained above, the initial predetermined amount of liquid pilot fuel being delivered to the particular cylinder under investigation is successively reduced by a first incremental amount until a first predetermined incremental change in the exhaust port temperature for that particular cylinder is observed. Based upon the particular exhaust port temperature versus liquid pilot fuel quantity profile of the particular cylinder under investigation, a particular predetermined incremental change in exhaust port temperature will be indicative of deteriorated cylinder performance based upon less than optimal ignition and combustion of the air/gaseous fuel mixture being supplied to that cylinder. Once this first incremental change in exhaust port temperature is observed, the amount of liquid pilot fuel being delivered to the particular cylinder under investigation is then successively increased by a second incremental amount until an incremental change in exhaust port temperature less than a second predetermined incremental change for that particular cylinder is observed. At this point, the liquid fuel injector control signal duration time for that particular cylinder is adjusted to deliver the last successive amount of liquid pilot fuel to such cylinder. This procedure establishes the minimum amount of liquid pilot fuel to be delivered to that particular cylinder in order to achieve optimum combustion of the gaseous fuel within such cylinder based upon exhaust port temperature. The control loop performing the operational steps of this process are executed in one cylinder at a time until all cylinders of the dual fuel engine are operating at or substantially near their minimum liquid pilot fuel quantity.
The present invention thus provides a method for controlling and adjusting the delivery of liquid pilot fuel to each cylinder of a dual fuel engine during a dual fuel operating mode so as to both minimize the quantity of liquid pilot fuel being delivered to each individual cylinder while, at the same time, ensuring that such minimum quantity o
Brown Scott C.
Fischer Jeffery T.
Willi Martin L.
Caterpillar Inc.
Kwon John
LandOfFree
Method for achieving minimum liquid pilot fuel delivery to... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for achieving minimum liquid pilot fuel delivery to..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for achieving minimum liquid pilot fuel delivery to... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2514059