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Open Access Publications from the University of California

Extending and Characterizing Fuel Flexibility in Small-Scale Power Systems

  • Author(s): McCoy, Christopher David
  • Advisor(s): Pisano, Albert P
  • et al.

The ultimate goal and hope for engines of the near future is the development of wide range fuel-flexibility within internal combustion engines. This research dissertation presents three innovations that have pushed the boundary of science and technology to enable this vision on the mini scale. First, the design and construction of a new small-scale, fuel flexible, engine dynamometer that allowed for precise measurement and control of mini engines operating on non standard fuels. Second, the fuel-flexible characterization of the O.S. Graupner Wankel engine and the successful production of output mechanical power between 10-500 W from a range of petroleum-based and bio fuels: gasoline, diesel, biodiesel, bioethanol and military-grade JP8 (among others). Lastly, a low-cost, multi-fuel switching system was designed and tested that controllably delivered a range of fuels to the engine and allowed for the first continual fuel-flexible operation using an array of fuels. In addition to these scientific contributions, it will be shown how the small-scale engine dynamometer and its peripherals were designed, constructed and tested such that future researchers can make advancements toward the ultimate goal enabling wide-range fuel flexibility on the small scale.

This work determined a number of the key parameters for small-scale fuel flexible engine operation (4.97 cc). Previous work only showed that fuel flexibility was possible in larger scale rotary engines and turbines--where operating conditions differ greatly from their smaller-scale counterparts. The present work extended the understanding of what engine parameters are critical for enabling fuel-flexible engine operation on this small scale and helped discover the strengths, weaknesses and opportunities of mini fuel flexible rotary engines which prior work had not described.

The design and construction of a new small-scale engine dynamometer was essential as no commercially available dynamometers on this scale existed and the legacy systems failed to capture all necessary engine data; especially those needed to characterize fuel flexibility. This dynamometer consisted of an engine mount and loading system, therequired sensors for measurement, the actuators to dynamically and repeatedly control engine and the integration of all these elements into a usable data acquisition system. The characterization consisted mainly of the maximum power outputs of the engine while running on specific fuels, the engine operating conditions during max power output, the stoichiometry ranges of each fuel in the context of the O.S. Graupner Wankel engine and output efficiencies. Other preliminary characterizations on emissions, combustion pressure and other typical engine tests were developed but not fully characterized but will be introduced.

The design and construction of a multi-fuel switching system was also integral to extending and characterizing fuel flexibility on this small scale. Early experiments only tested fuels independently and switched between them by hand. However, future systems would need to be able to change fuels on-demand and sequentially in real time. Therefore, a system that could accommodate the storage of multiple fuels and then deliver them reliably to the engine at the click of an on-screen fuel selector button was built, better syncing the fuel data with the engine performance data.

The resulting fuel-flexible engine characterization system was then tested amongst a variety of liquid hydrocarbon based fuels in order to create a fuel-flexible engine mapping for a Wankel engine of 4.97 cc displacement. During multi-fuel combustion, the following parameters were measured in an effort to fully characterize this engine: engine torque, mass flow rate of ambient air intake, stoichiometry, ambient temperature and humidity, ambient pressure, engine speed, mass fuel flow rate, engine housing temperature, engine exhaust temperature and loading brake temperature and the fuel selection. This data collection was possible through the design and integration of the LabVIEW data acquisition system architecture in concert four input / output devices: the NI-USB-6221, NI-USB-9162 and two ArduinoUNO microcontrollers. The design and integration will be fully described along with the new system potential and shortcomings.

In addition to the data acquisition, the system was also designed to enable future real-time control using conventional low-cost model engine servos such that the system could be fully automated. In the current system, there are eight actuation devices that control the throttle position, the glow plug heat, the fuel to air ratio, the dynamometer brake and four electrovalves that control the delivery of each fuel. The mechanical design and construction of all these control mechanisms are also described along with their added potential to enhancing fuel flexibility and opportunities for future improvement.

The fuel flexible dynamometer system, multi fuel switching system, data acquisition and system control enabled fuel flexible operation of a Wankel engine of 4.97 cc displacement. The maximum mechanical power produced from Gasoline, Glowfuel (methanol+nitromethane mix), JP8, Diesel and Biodiesel were 334 W, 508 W, 313 W, 239 W and 322 W respectively. Methanol did not require active glowplug power while the 87 octane, diesel and JP8 fuels did. Good throttle response for both Methanol and JP8 was observed however the 87 octane operation, there was little to no throttle response during combustion. This dissertation research clearly demonstrates that small-scale Wankel rotary engines are fuel flexible across at least 6 different fuels: methanol, gasoline, diesel, JP8, biodiesel and ethanol.

This dissertation is broken down into six separate chapters: Chapter 1 Introduction that describes the motivations and background of this research, Chapter 2: Theory which gets the reader up to speed with the relevant engineering concepts, Chapter 3: Experimental Setup Design which describes how the fuel flexible characterization system was built, Chapter 4: Experimental Results which succinctly presents all data key data collected during this research, Chapter 5: Discussion and Analysis which are the conclusions drawn from the captured data and Chapter 6: Conclusions which briefly reiterates the key developments presented in this dissertation.

It is the hopes of the author that this research serves as a stepping stone in future development efforts and allows science and technology to arrive at a point where wide range and robust fuel flexibility is possible.

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