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Precision In-Cylinder Pressure Sensor System for Heavy Duty Diesel Engines


OBJECTIVE: Develop a high data-rate real-time pressure measurement system to continuously measure combustion pressure in diesel engine cylinders, which is affordable, durable, and accurate, for future use in real-time adaptive engine controls of fuel injection. BACKGROUND/DESCRIPTION: Unlike commercial diesel engines which are typically designed to operate on a single fuel such as U.S. ultra-low sulfur highway diesel (ULSD), military engines must be able to operate on a variety of distillate fuels, typically jet and worldwide diesel fuels, due to worldwide deployments. Most U.S. military diesel engines are adapted commercial engines and have no ability to compensate for the varying properties among jet (JP-8, JP-5, Jet-A1, and others) and worldwide diesel fuels. Jet fuels, which are otherwise similar to arctic diesel fuels, pose a particular problem because the cetane index, a measure of a diesel fuel"s tendency to ignite upon injection, is not controlled in jet fuels (except in recent synthetic jet fuel blend specifications) and is typically low. A low cetane index causes power loss, inefficient combustion, poor low-temperature starting and in severe cases, damage due to excessive chamber pressures. Real-time adaptive electronic engine controls could manage these effects by adjusting diesel fuel injection timing and rate according to fuel combustion performance, but a high data-rate system to continuously measure combustion pressure is needed to provide input data. The system must be affordable, durable and accurate, and detect explosive combustion events which can occur with very low cetane fuels. By closely monitoring and controlling combustion pressure in real-time, a military engine control will adapt on-the-fly to fuels with a broad range of ignition properties, allowing military engines to attain high power output and efficiency despite variable fuel properties. Sensors with the desired sensing capability are now used in diesel engine laboratory research, but they are large, costly and not designed for use in vehicles. Because the integral of combustion pressure and volume reveals the work produced in a single firing event, data from the high-speed pressure sensor makes it possible for an engine control, using crank position data to determine piston travel, to determine precisely how to adjust diesel injection timing to get maximum efficiency from an injected unit of fuel. When used in commercial engines, high speed precision pressure measurement will allow engine control units to better control nitrogen oxide, hydrocarbon and smoke emissions by precisely managing the fuel injection timing and quantity to attain the optimal pressure-temperature profile in each combustion event. This will enable smaller exhaust gas recirculation (EGR) flows, reducing the parasitic power burden used for EGR cooling and recovering some of the engine efficiency that is currently lost to EGR implementation. PHASE I: Design 1. The contractor shall design a high data-rate pressure sensor that continuously and directly measures individual cylinder combustion pressures in diesel engines, and the corresponding data acquisition system. 1.1 The sensor shall measure with +/- 1% accuracy over the pressure range 0-350 bar, and shall be capable of measuring at 27,000 readings per second, equivalent to one measurement per degree of crank angle rotation in an engine running at 4500 revolutions per minute. The sensor shall also be able to measure a pressure rise rate of at least 810 bar per millisecond in order to detect explosive combustion events. 1.2 The sensor shall be designed for a working life of 10,000 hours. 1.3 The sensor tip shall have no more than a 4 millimeter (mm) diameter exposed face in the combustion chamber, shall not protrude into the combustion volume and shall not alter fuel injection spray patterns. 1.4 The installed sensor shall filter out the effects of engine vibration, and must be immune to carbon fouling and combustion chamber temperatures in its mounting location. 1.5 The contractor shall show by analysis and experiment that the physical principles of the sensor design are feasible for use in a cylinder pressure sensor. The contractor shall build a test article that is based on the sensor"s operating principle, and show that the sensor is feasible at room temperature and the intended operating pressures and frequencies. 1.6 The contractor shall design a data acquisition system for the high data-rate sensor that can receive a total of up to 27,000 measurements per second from up to twelve engine cylinders simultaneously and can output digital pressure data for each engine cylinder in a form usable by an electronic diesel engine control system. The data acquisition system shall be designed to operate on 24 volts DC power. 1.7 The data acquisition system design shall include cabling or other communications means between the sensors and the data acquisition system and the cabling shall be designed to be durable in a heavy vehicle engine compartment environment. 1.8 The complete sensor and data acquisition system shall be designed for a target cost of $300, based on a variant intended for installation in a six-cylinder commercial truck engine. PHASE II: Demonstration 2. The contractor shall build and demonstrate the sensor and data acquisition system designed in paragraphs 1.1 -1.6 above. 2.1 The sensors and data acquisition system shall be demonstrated on a multi-cylinder diesel engine in a test cell environment. The demonstration will not require any actual control of the engine or interaction with the engine controller. 2.2 The contractor shall demonstrate that the data acquisition system can support twelve sensors in operation, but demonstration on an engine is not required. CONTRACT DELIVERABLES: a. Monthly technical reports in letter format, with a financial report of actual vs planned spending. b. Final technical report with conceptual drawings of the sensor and cabling. c. One complete set of six sensors, and a sensor data acquisition system for government testing. d. Documentation of the algorithms used for the data acquisition system, the data output format, and a government-editable version of the data acquisition system software with documentation sufficient to enable government engineers to load, operate and save modified versions of the software.
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