Thrust 2: Compactness

Title

2B.2: Miniature HCCI Free-piston Engine Compressor

Project Leader

Prof. David Kittelson (UMN)

Statement of Project Goals

The objective of this project is to continue development a compact high efficiency air compressor providing 10 W of pneumatic power that can be used for the Test Bed 6 ankle foot orthosis (AFO) and for other applications needing a tiny fluid power supply. The power source is a free piston engine operating in a homogeneous charge compression ignition (HCCI) two-stroke cycle, integrated with a free-piston air compressor. This engine compressor package, coupled with a fuel tank, will provide much higher power density and energy density than a battery - motor package, thus enabling a more compact design and longer run time of tiny fluid power systems.

Project's Role in Support of the Strategic Plan

This project is necessary to achieve Goal 3 of the CCEFP: portable, un-tethered, human-scale application. The targeted transformational barrier for accomplishing this goal is the lack of compact fluid power systems. The project is specifically directed towards Test Bed 6 with its stringent requirements for wearable components. The power requirements for the active AFO drive the engine design for this project. Our initial target is a fluid power output at the lower end of the orthosis range, 10 W but the concept will also work for delivering higher power.

Description and Explanation of Research Approach

The approach for the development of the engine compressor is based on an integrated program of testing and modeling. The design of prototype engines is based on mathematical modeling which is supported by testing of components from a very small conventional engine, and testing of prototypes themselves. With the experimental results, appropriate models with fitted parameters can be chosen to better simulate the engine, which in turn will guide the design and optimization of further generations of prototypes. These optimizations will include improvements in compactness and efficiency as well as reductions in emissions, noise, and heat rejection.

Figure 1: Miniature HCCI Free-Piston Engine design concept (left) and first generation prototype (right)

References

1. Tian L, Kittelson DB, Durfee WK. Miniature HCCI Free-Piston Engine Compressor for Orthosis Application. Small Engine Technology Conference, Penang, Malaysia, Nov. 2009.

2. T. Ogawa, Y. Kawaguchi, "Performance testing of 5CC glow-ignition four-stroke engine", proceeding of 2007 ASME/JSME thermal engineering summer heat transfer conference, Vol. 3 pp 807 - 814, 2007.

3. R. Raine, H. Thorwarth, "Performance and combustion characteristics of a glow-ignition two-stroke engine", SAE Technical Paper Series, paper number 2004-01-1407, 2004.

4. H. Ma, K. Kar, R. Stone, R. Raine, H. Thorwarth, "Analysis of combustion in a small homogeneous charge compression assisted ignition engine", International Journal of Engine Research, 2006, Vol. (7), pp 237 - 253.

5. J.B. Heywood, E. Sher, "The Two-Stroke Cycle Engine: Its Development, Operation and Design", published by Taylor & France, 1999, ISBN: 1-56032-831-2

6. L. Tian, D.B. Kittelson, W.B. Durfee, "Experimental Tests and Simulations of A 1.5 cc Miniature Glow-Ignition Two-Stroke Engine", SAE Technical Paper, paper number 2010-32-0018, 2010