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Adaptive Inter-Cylinder Output Balancing System (AICOBS)


OBJECTIVE: Develop an in-vehicle, software system, for an electronically-controlled diesel engine fuel system, to adaptively reduce inter-cylinder variability in output, in real-time, resulting in improved engine output, reliability, and fuel economy. DESCRIPTION: All multi-cylinder internal combustion engines exhibit imbalance in power output between cylinders. This is due to necessary hardware design compromises as well as manufacturing variances in engine components. An example of the former is the difference in the length and shape of intake manifold runners, which can lead to inter-cylinder variation in mass of air delivered, as well as differences in mixture motion. An example of the latter is manufacturing tolerance differences in individual fuel injectors, leading to variation in mass of fuel delivered to each cylinder. The variation in output between cylinders results in uneven acceleration of the crankshaft during each rotation. This causes vibration which can lead to accelerated wear and potential early failure of engine components. In addition, the secondary effects of variation in the combustion event within each cylinder are differences in temperature and pressure of the combustion and exhaust gases. If fueling mass and timing are not adjusted for each cylinder individually, when even one cylinder is approaching a dangerous operating condition, the output of rest of the cylinders might have to be maintained at a sub-optimal level, in order to protect the one"bad"cylinder. This can mean that the potential for higher output and/or better fuel economy for the engine as a whole is being limited. One widely-used measure of engine output is Indicated Mean Effective Pressure (IMEP). This metric is useful because it enables comparison of engines of differing size within a general design class (turbo-diesel, naturally-aspirated gasoline, etc.) Variations of 5% to 10% (depending on operating condition) in IMEP values between cylinders have been noted in diesel engines using DF2 fuel. Even higher variations have been seen for the same engines running JP8. The target for this project is to reduce inter-cylinder imbalance to below 2% under all operating conditions, regardless of fuel. In order to mitigate the effect of this imbalance, manufacturers will sometimes introduce engine control software calibration settings that vary the mass and timing of fuel delivered to individual cylinders, under prescribed operating conditions. However, when this is done, it is based on measured data acquired from a limited sample of engines tested on dynamometers. The result is a one-size-fits-all approach that remains static in the field, and cannot adapt to the variation between individual engines, or all of the potential environmental conditions that might be encountered. An alternative approach that has also been tried is to install in-cylinder pressure sensors that are capable, with appropriate analysis software, of quickly and accurately characterizing the combustion event. This system is quite capable of finding inter-cylinder imbalance so that it can be mitigated by uniquely tailoring the fuel delivery to each cylinder. Unfortunately, this system is expensive, both at installation and in terms of reliability and maintainability. An approach is required that can react to variations in inter-cylinder output in real-time, on the vehicle in the field, and continually adjust engine fueling parameters to reduce the variation, using only the instrumentation and electronic control systems installed by the manufacturer, by developing an intelligent signal processing algorithm, capable of being implemented in software that can be run in the manufacturer's engine control module. PHASE I: Complete a feasibility study that should determine the technical and commercial merit of developing a Adaptive Inter-Cylinder Output Balancing System (AICOBS). This effort shall fully develop an initial concept design, establish programmatic (cost, schedule and performance) goals, and deliver a final technical report detailing the AICOBSconcept. This initial concept must be designed to: 1) be"adaptive", meaning capable of reacting to the actual inter-cylinder imbalances being experienced by the engine (as opposed to being statically calibrated in advance), 2) be"real-time"meaning the recognition of the imbalance and the corrective reaction must occur within a sufficiently short time interval that inter-cylinder balance is maintained under all expected operating transients, 3) use only the standard sensors and actuators present in a typical electronically-controlled fuel system, 4) be capable of being run in a commercial engine control module along with all of the manufacturer's other control software, without negatively impacting the system's capability or throughput. PHASE II: This effort will culminate in two well-developed Adaptive Inter-Cylinder Output Balancing System (AICOBS) prototypes. The first prototype will be fabricated using the Phase I concept design. The performance goal for the first prototype will be 2% variation in IMEP across all cylinders under steady-state operating conditions. The second prototype will be improved through a testing and redesign process. The performance goal for the second prototype will be 2% variation in IMEP across all cylinders under steady-state and transient operating conditions. 1. Produce a prototype AICOBS based on the Phase I concept design. 2. Establish actual system performance through physical testing (and compare the results to the original performance goals), then document"Lessons Learned". 4. Redesign the Phase I concept while applying the"Lessons Learned"from performance, testing. 5. Fabricate a 2nd generation AICOBS prototype based on previous redesign applying the"Lessons Learned"approach. 6. Validate expected performance through testing (and compare to performance goals). This effort shall deliver: 1. Demonstration of Phase I AICOBS concept prototype, after testing is complete. 2. Demonstration of second generation redesigned AICOBS prototype after testing is complete. 3. A final technical report detailing the 2nd generation redesigned AICOBS prototype. PHASE III: Inter-cylinder balancing is a technology that would provide enhanced performance, fuel-economy, and reliability in all military ground vehicles that currently utilize digital electronic control for fueling. Most commercial diesel-powered vehicles already utilize electronic fueling control. Inter-cylinder balancing has been researched and tested by the big commercial manufacturers, but has not been put into production because of the high cost of the in-cylinder sensor hardware. This effort envisions a software-only solution, using sensor hardware that is already installed on commercial vehicles that feature electronic fuel control. Commercial vehicles would see the same benefits as military vehicles, namely enhanced performance, fuel economy, and reliability. These benefits would be realized without the significant additional expense of additional sensor hardware.
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