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Cetane Sensor for Remotely Piloted Aircraft (RPA) Propulsion Systems that Operate on Heavy Fuel


OBJECTIVE: To develop and demonstrate a Cetane sensor for RPA internal combustion engines (ICE) that operates on heavy fuel. DESCRIPTION: A new generation of remotely piloted aircraft (RPA) engines has been under development for the last eight years. Many of the RPAs that the military currently uses were designed for nonmilitary purposes and many operate on aviation gas (Avgas). The military RPA community has been working to convert engines from gasoline to heavy fuels such as JP-5, JP-8 and Jet A for a one fuel in the field concept that allows the military greater logistics flexibility. The development of an improved Cetane sensor will provide a fast, reliable method to analyze fuels in real time to optimize the RPAs ability to meet mission requirements. The Cetane sensing capability will improve RPA on-station availability, overall capability, and avoid the costs associated with laboratory analyzes, shipments, or packaging that may not represent the fuel properties located in the field. Diesel fuels such as Diesel #2 are manufactured with a required Cetane number. ASTM D975 specifies a minimum of 40. Most Diesel #2 in the U.S. is 42-45. The specifications for JP-5, Mil-DFL-5624, JP-8, Mil-DFL-83133P-8, and Jet-A, ASTM D1655, have no Cetane rating. Cetane is important for compression ignition engines, and has no affect on turbine engine performance, which is what these fuels were designed for. Using fuels with too low of a Cetane number in a diesel engine will result in a rough-running, hard-to-start, or a non-running engine. There have been a number of internal combustion (IC) engine programs started by the military services that are being designed to use heavy fuel. Some of these developments are for spark-ignited (SI) engines and some are for compression ignition (CI) engines. CI engines rely on Cetane as the property that gives a diesel engine the ease of igniting the air fuel mixture. The higher the Cetane number of the fuel, the more easily it combusts. The ability of the military to run both SI and CI engines on heavy fuels such as JP-5, JP-8 and Jet-A with optimal performance requires an ability to calculate the Cetane rating of the fuel as it is being used. Many of the new developmental RPA engines are being designed for direct injection. Therefore, the fuel injection system will be controlled by a computerized control system. This will enable the capability to change injection timing in near real time based on the Cetane number that is being determined and that data will be sent to the engine control system. This will allow engine performance to be optimized when using different sources of JP-5, JP-8, and Jet-A fuels. During the Phase I effort, Cetane sensor concepts should be proposed that provide adequate performance in the measurement of Cetane for JP-5, JP-8, and Jet A. The sensor must be made small enough to be part of the RPA system and be able to make real time calculations of the Cetane properties of the fuel being utilized. Phase II will fully develop, fabricate, and demonstrate the system in a ground test environment with designs integrated into a RPA propulsion system. Phase III options should integrate the system into a new generation propulsion system to be used by the military and to test system performance with flight tests in an RPA mission environment. It is also appropriate to investigate methodologies that correlate engine performance measurements with Cetane values. Fuel detonation propensity, burning rate, and pressure developed are related to fuel characteristics and directly affect dynamic performance. Performance measurements can include, but not limited to, combustion pressure, timing measurements and engine dynamic torque measurements. PHASE I: Demonstrate the feasibility of an innovative Cetane sensor in a small package through modeling, empirical, pragmatic, and chemical analyzes of the fuel. The sensor concept should include the size and weight estimation of the sensor and the expected performance. The sensor should have the capability to output the Cetane rating of the fuel to the RPA control system. PHASE II: The Phase II effort will fully develop and fabricate the sensor system design from Phase I and demonstrate it in a ground-based environment. Ideally, the demonstration should use an in service or development engine that is aimed at the RPA environment. Different sources of fuel should be used for demonstration. PHASE III: A Cetane sensor with the above characteristics could be highly marketable in the commercial sector to optimize the running of diesel engines for both optimum performance as well as decreased emissions. REFERENCES: 1. G. Smith, G. Minkiewicz, F. Eisert, P. Meitner, J. Jerovsek, M. Boruta, and P. Dahlstrand,"Conversion of Small RPA Engines from Gasoline to Heavy Fuel,"AUVSI Conference 2011, 18 August 2011, Washington DC. 2. P. Schihl, L. Hoogterp, H. Pangilinan, E. Schwarz, and W. Bryzik,"Modeling JP-8 Fuel Effects on Diesel Combustion Systems,"RDECOM-TARDEC Warren, MI. 48397-5000. 3. NTIS Report on"Octane-Cetane Relationship,"Army Mobility Equipment Research and Development Center, Report Number 33, March 1974.
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