Characteristics of Combustion in Small Rotary Engine Chambers

Overview • • Rotary Engine Project Introduction Rotary Engine Review Research Motivation and Approach Experimental Set-up and Results – Pressure Rise – Flame Speed • Experimental Conclusions • Commercialization Opportunities © 2005 University of California Prepublication Data Fall 2005

Rotary Engine Project Introduction • Portable power generation 50 -200 W • Operates with liquid fuel • Higher specific energy than batteries © 2005 University of California Prepublication Data Fall 2005

Rotary Engine Introduction • Triangular shaped rotor revolves directly on eccentric shaft • Operates on four-stroke cycle • Combustion pocket is cut of rotor face 1 2 intake port spark plugs 4 exhaust port 3 © 2005 University of California Prepublication Data Fall 2005

Research Motivation • Develop combustor design and determine operating conditions in parallel with engine development • Isolate combustion event from engine effects • Understand limits of combustion at small scale – Pressure rise – Flame propagation speed © 2005 University of California Prepublication Data Fall 2005

Research Approach Original static combustion chamber duplicates the Wankel engine geometry at top dead center. Volume = 278 mm 3 22 mm 7. 9 mm 1. 6 mm © 2005 University of California Prepublication Data Fall 2005

Experimental Apparatus Improved chamber allows for quick changes to the size of the chamber

Experimental Apparatus The chamber is filled with a fuel air mixture and ignited. Pressure

Preliminary Experimental Conditions The Pressure, Temperature and Chamber Geometry are varied to simulate engine conditions. Test Variable • Initial Pressures 0, 40, 80 psi • Initial Temperatures 25, 75, 100ºC • Chamber Size 8, 6, 4 mm © 2005 University of California Engine Parameter Compression Ratio Thermal Management Heat Loss Prepublication Data Fall 2005

Pressure Data Pressure ratio is defined as the peak pressure divided by the initial

Experimental Data Pressure ratio drops slightly as initial pressure is increased due to more leakage at higher pressures. o 8 mm chamber, 100 C, butane/air F = 1. 0 © 2005 University of California Prepublication Data Fall 2005

Experimental Data Pressure ratio drops as initial temperature is increased due to reduced energy density at higher temperatures. 6 mm chamber, 4. 4 atm, butane/air F = 1. 0 © 2005 University of California Prepublication Data Fall 2005

Experimental Data Pressure ratio increases as chamber width is increased due to reduced heat loss in larger chambers. o 4. 4 atm, 65 C, butane/air F = 1. 0 © 2005 University of California Prepublication Data Fall 2005

Comparison with Chemical Equilibrium Model Experimental pressure rise is 2 -4 times lower than predicted by STANJAN program. STANJAN Experiments Adiabatic Non-Adiabatic Infinite time to Finite reaction reach equilibrium time Constant mass © 2005 University of California Mass loss Prepublication Data Fall 2005

Optical Instrumentation High speed video was taken of the flame front. The Schlieren apparatus measures differences in index of refraction to determine the flame front. Point Light Source Beam Splitter Combustion Xenon Light Pin Hole Beam chamber with Splitter Source mirror Flat Mirror Chamber Detail of Color Slide High–speed camera High Speed Camera Collimating Mirror © 2005 University of California Collimating PC for mirror control and Rainbow data storage slide Prepublication Data Fall 2005

Schlieren Images for Butane-Air mixture Sequential schlieren images at T = 50 o. C

© 2005 University of California Prepublication Data Fall 2005

Flame Position Data position (m) Propagation speed is calculated using the sequence of schlieren

Propagation Speed Propagation speed is the sum of the burning speed, expansion speed and leakage of gas through inlet and outlet holes. up = Sb + ugas + uleak Sb = freely propagating flame speed ugas = expansion speed due to difference in density between reactants and products uleak = apparent velocity due to mass loss at inlet and exit © 2005 University of California Prepublication Data Fall 2005

Effect of pressure Propagation speed increases at higher pressures due to increased leakage flow. o 8 mm chamber, 25 C, butane/air F = 1. 0 © 2005 University of California Prepublication Data Fall 2005

Effect of Temperature Propagation speed is relatively constant due to the limited temperature range tested. 8 mm chamber, 6. 4 atm, butane/air F = 1. 0 © 2005 University of California Prepublication Data Fall 2005

Effect of chamber width Propagation speed decreases for smaller chambers due to increased heat

Experimental Conclusions • Dynamic pressure was measured inside the chamber and compared to an adiabatic model. • Pressure rise is strongly dependent on chamber size and temperature, weakly dependent on pressure. • The flame propagation speed has been measured using the schlieren imaging technique. • Propagation speed is also strongly dependent on chamber size and pressure, but not on temperature in the temperature range tested. • Further work needed to determine relative effects of heat loss, mass loss and incomplete combustion. © 2005 University of California Prepublication Data Fall 2005

Commercialization Opportunities Assuming technical and manufacturing limitations are addressed, what is the market for portable generators? Assumptions: Ideal Mini-REPS Engine Power: 200 W Efficiency: 20% Cost: $200 Weight: 1 kg Run time: 6 hrs © 2005 University of California Prepublication Data Fall 2005

Market Segments Four market segments have been identified. Military Portable tools Recreational power Backup power www. defense-update. com, www. hondapowerequipment. com, www. upcc. com, www. blackanddecker. com © 2005 University of California Prepublication Data Fall 2005

Market Entry Military applications can absorb high initial cost. To enter mainstream market, focus on reducing price Military Recreational and backup power Portable tools From Geoffrey Moore: Crossing the Chasm © 2005 University of California Prepublication Data Fall 2005

Customer Needs Each segment values different attributes. Portable tools light Military Recreational power expensive cheap Backup power heavy www. defense-update. com, www. hondapowerequipment. com, www. upcc. com, www. blackanddecker. com © 2005 University of California Prepublication Data Fall 2005

Customer Needs Each segment values different attributes. 1 Portable tools 4 light Military Recreational power 3 expensive cheap heavy 2 Backup power www. defense-update. com, www. hondapowerequipment. com, www. upcc. com, www. blackanddecker. com © 2005 University of California Prepublication Data Fall 2005

Conclusions • A static combustion chamber has been built to investigate combustion in small-scale chambers • Initial pressure and temperature were controlled to simulate engine operating conditions • Dynamic pressure was measured inside the chamber and compared to adiabatic model • The flame propagation speed has been measured using the schlieren imaging technique • The early market consists of military applications which are not sensitive to cost • To open new market for portable power applications, initially trade performance for cost, then improve performance © 2005 University of California Prepublication Data Fall 2005

Thank you © 2005 University of California Prepublication Data Fall 2005

Future Work • Determine effect of ignition energy on ignition and flame speed • Measure effect of glow plug on ignition and ignition energy • Sample and analyze combustion products to correlate with combustion efficiency model • Include heat loss and mass loss in combustion efficiency model • Measure effect of flowing mixtures on ignition • Use multiple fuels including methanol and hydrogen • Compare static results with engine data © 2005 University of California Prepublication Data Fall 2005