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Direct Injection Systems for Small UAV Engines

Description:

OBJECTIVE: Develop and demonstrate an advanced high pressure heavy fuel (JP-8) injection system for Unmanned Aerial Systems/Unmanned Ground Systems (UAS/UGS) application, capable of performing multiple injections per cycle for engines in the size of 2 to 50 horsepower (hp). 

DESCRIPTION: This effort is to develop a fast responding, light weight, direct injection system to operate within the fuel’s ignition delay time for UAS/UGS application. These systems must be applicable to engines that are 2 to 50 hp, either reciprocating or rotary. A technical challenge associated with the conversion of gasoline engines to heavy fuel (JP-8) is the avoidance of knock. An approach used to avoid knock is to operate within the fuel’s ignition delay time; hence to employ direct combustion chamber injection. The challenges of the reciprocating engine are to avoid end gas knock (auto ignition occurring in the end gas after spark) and to inject the fuel very late into the cycle. The challenges for the rotary engine are atomization and the avoidance of wall quenching due to its combustion chamber shape.Delaying the injection process causes higher pressure rise rates which can exceed the engine’s design capabilities. An injection system that offers fast response and multiple injections per cycle may alleviate excessive pressure rise and the avoidance of knock. Good combustion control eliminates many durability issues from overloading, shock, and combustion deposits. The shape of the combustion trace can be tailored through multiple injection pulses and combustion deposits can be controlled with better atomization and fuel patterns. Hence an injection system that offers fine atomization, fast response, and multiple injections per cycle is needed. Note - Present day state-of-the-art direct injection systems used for automotive application are solenoid type and operate up to 3000 psi with 0.010" orifice and have response times (opening delays) of 0.5 msec. 

PHASE I: Define and develop innovative fuel injection technologies that will result in improvements to the direct injection process for reciprocating and rotary UAS engines (fuel injector design). Bench tests of fuel system components operating at designed pressures and quantification of injection spray pattern is desired (fuel injector operation). The fuel injection system should have the capability to perform multiple injections per cycle and at engine operating speeds up to 10,000 rpm. CFD to define the optimum fuel-air contour should be considered. Small scale bench testing is appropriate to determine feasibility of concept. 

PHASE II: Demonstrate and validate the performance of the Phase I technology in a laboratory environment on a representative engine. Engines should be UAV platform of the Group 2 and Group 3 UAV class. Further analytical modeling (CFD) and spray tests must supplement engine testing. Demonstration of direct combustion chamber injection with rate shaping (multiple injections per cycle) is required. The avoidance of knock while operating on JP-8 and delivering equivalent power is the desired outcome. 

PHASE III: This technology has additional transition opportunities in the commercial sector. Companies could incorporate the injectors, high pressure supply pump, feed pump and controller with harness to optimize the fuel injection associated with the engines. This could lead to cleaner combustion that could greatly increase the life of the engine. Further, advanced direct injections systems have the potential to reduce specific fuel consumption. Small engine application for UAS, electrical power generation, and RV usage are potential markets of application. 

REFERENCES: 

1: "Fundamental Spray and Combustion Measurements of JP-8 at Diesel Conditions," L. Pickett and L. Hoogterp, SAE Paper No. 2008-01-1083, 2008.

2:  "Piezoelectricity: Evolution and Future of a Technology," Chapter on Piezoelectric Injection Systems by R. Mock, K. Lubitz Authors: Prof. Dr. Walter Heywang,Dr. Karl Lubitz,Wolfram Wersing ISBN: 978-3-540-68680-4 Publisher: Springer, Nov 2008.

3: "Common Rail Injection System for High Speed Direct Injection Diesel Engines" by Guerassi N. and Dupraz P., SAE Paper 980803, Detroit, MI 1998.

KEYWORDS: Atomization, Emulsification, JP-8, Knock, Ignition Delay Time, Common Rail, Rate Shaping 

CONTACT(S): 

Gregory Minkiewicz 

(937) 255-1878 

gregory.minkiewicz@us.af.mil 

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