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Improved Turbochargers for Small IC Engines

Description:

OBJECTIVE: Develop improved turbochargers and turbocharger installations to improve engine performance in areas such as takeoff power, endurance, altitude capability, exhaust scavenging, noise suppression and power enhancement for engines from 2 horsepower up to 20 horsepower (hp). Improve propulsion system thermal efficiency by using exhaust gas pressure for two stroke and four stroke engine application. 

DESCRIPTION: This topic seeks turbochargers for small engines in the 2 to 20 hp range. Included are turbochargers for two stroke engines used for UAS application. The turbochargers must be light weight, durable, and efficient. Turbocharger system development for the current and future fleet of unmanned aerial vehicles (UAVs) and small aircraft is underrepresented. Improvements are needed in installed metrics such as takeoff power, endurance, altitude capability, as well as component-level metrics such as extended pressure ratios, efficiency and viability of small engine turbochargers, improved engine operability, or turbo surge margin. Desired for small UAV engines are increases in service ceiling, or conversely, the ability to start at higher altitudes than normal aspiration allows. Also of interest, is the ability to "turbonormalize" engine conditions; to achieve power at altitude. Specific categories of engines include, (1) engines below 20 hp, including 2-strokes, (2) 2- and 4-stroke engines below 20 hp, and (3) diesel engines. Present day state-of-the-art turbochargers are used on 50 shp engines with an efficiency of 75 percent - this effort seeks smaller turbochargers (see Garrett Turbocharger website). 

PHASE I: Produce a feasibility study and development plan with realistic goals and schedule for an efficient small engine (2-20 hp) turbocharger. Applications should be oriented to aviation propulsion systems with the intent to increase needed or desired operational capabilities, or to leverage and extend existing automotive technology into aviation-specific areas. Studies should include the effects and consequence of turbocharging small two-stroke engines from 2 to 20 hp; on installation, performance, lubrication, acoustic & vibration effects; include preliminary aerodynamic analysis depicting compressor and turbine performance. (CAA: Q5 - Phase I narrative does not define what needs work - requesting the production of a feasibility study seems more as a planning activity, not R&D. Recommend that the Phase I demonstrate concept feasibility of the proposed technology.) 

PHASE II: Develop and test a working, proof-of-concept turbocharger. Turbocharger is required to be demonstrated on small UAS engines. Further, compressor and turbine maps should be developed. The proof of concept must consider rotordynamics analysis and bearing lubrication (oil lubricated and air). Engine testing is required for two stroke and four stroke UAV application supplemented with CFD optimization for compressor and turbine performance. 

PHASE III: Develop and test an actual production-intent turbocharger installation, ideally with flight testing of a representative aircraft. Commercialization would be in the recreation and UAV market which use small engines in the 2 to 20 hp range. 

REFERENCES: 

1: "Fundamentals of Turbocharging," Nicholas C. Baines, Publisher: Concepts ETI, Inc., 2005.

2:  "Aero and Vibroacoustics of Automotive Turbochargers," Nguyen-Schäfer, Hung, Springer-Verlag Berlin Heidelberg, 2013.

KEYWORDS: Turbocharge, Forced Induction, Rotordynamics, Pressure Ratio, Efficiency, Air Bearings 

CONTACT(S): 

Gregory Minkiewicz 

(937) 255-1878 

gregory.minkiewicz@us.af.mil 

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