1
ROTARY STEAM ENGINE:
Viability of the SpinDyne Shields Engine
Allgood, David
Bass, Brent
Buck, Jesse
Diaz, Christian
Ewa, Kenneth
Gillispie, Shane
Hargett, Michael
Hinson, Dylan
Labonte, Jonathan
Lawrence, Andre
Spruill, Franklin
MAE 435
Final Report
Dr. Sebastian Bawab
06 MAR 2014
Table of Contents
Abstract……….…………………………………………………………………………….…..…1
Introduction…..……………………………………………….………………………………...…2
Methods….……………………………………………………………………………………...…4
Boiler/Heat Exchanger…………………………………………………………………….4
Engine…………………………………………………………………………….……….5
Combustion…………………..……………………………………………………………6
Condenser/Pump…………………………………………………………………..………7
Finite Element Analysis…………………………………………………………………...8
Results……………….…………………………………………………………..…………….…..9
Discussion…….…………………………………………………………………………………...9
References……….……………………………………………………………………………….11
Appendix……….………………………………………………………………………………...13
Figures…………………………………………………………………………...…….…13
Gantt Chart…...…………………………..………………………………………………19
Budget…...…………………………………………………………………………..…...20
Programs....……………………………………………………………………..………..21
Equations…………………………………………………………………………..……..33
List of Figures
Figure 1. PV Diagram……………………………………………………………………………13
Figure2.SpinDyne's Rotary Steam Engine...... 13
Figure3. Flow Chart of the Complete Engine System…..…..………..………………………....14
Figure4a. Open Cell Metal Foam...... 14
Figure 4b. Closed Cell Metal Foam…….………………………….………...………………..…14
Figure 5. Results from Combustion Program………..…………………………………….…….15
Figure 6. Graphs of Combustion and Condenser Program…...…..……….……………………..15
Figure 7. Results of Condenser Program…………..……………………….……………………16
Figure 8. Combustion Results for Diesel…………..……………………….……………………16
Figure 9. Cost of Selected Fuels……….…………..……………………….……………………17
Figure 10. Engine Results……………….………..……………………….………..……………17
Figure 11. Engine Graphical Results………………..…………………….…………..…………18
Figure 12. Gantt Chart………………………………………………………………………..….19
Figure 13. Budget………………………………………………………………………...…..….20
1
ABSTRACT
SpinDyne has introduced a new design of a rotary steam engine that will be expected to compete with the current efficiency and emission standards of the modern combustion engine. Analysis of the engine must be done to determine if it is viable replacement for the combustion engine. A thermodynamic analysis of the engine is ongoing, assuming the engine runs on an ideal Rankine cycle for initial estimates, and a second analysis will be performed assuming non-ideal conditions. A study of the combustor and the effect of various fuels on heat input were also completed. A thermodynamic analysis of the condenser, pump, and heat exchangers will be done. For a complete analysis, there will also be a finite element analysis done to determine critical stress areas.
INTRODUCTION
The steam engine was invented in the 1700’s by James Watt. The engine cut fuel consumption by 75% creating a practical solution to energy problems and has been used in nearly every imaginable industry [1]. Steam engines use heat to convert the working fluid (water) into steam where it is then converted from thermal energy to mechanical power. The steam engine is a major contributor to the American Industrial Revolution. Steam powered ships and cars were in existence during the early 1900s, however, this technology has not been directly applied to vehicular propulsions since [2]. The first rotary steam powered machine was built in 1760, merely designed to pump water out of coal mines [3]. Following this invention, several successive modifications and patents were made to improve its efficiency and design. In 1804, the design of a high-pressure, non-condensing steam engines was introduced and used to power the first amphibious vehicle [4]. This design broke the configuration of the steam engine into individual modules with working components independent of one another; this particular configuration has come to be the most widely acceptable method in steam engine design.
The internal combustion engine such as gasoline, diesel and gas turbine engines replaced the steam engine in most industrial and automotive industries. The internal combustion engine was a more compact method for providing motive force and was more user friendly than steam engines of the time. Internal combustion engines require a specifically refined fuel and led to a number of harmful emissions. Carbon emissions (carbon monoxide and carbon dioxide) from internal combustion engines was among the leading causes of greenhouse gases from 1960-2008 [5]. Limiting carbon-based fuel usage by use of steam power is a plausible reality in personal transportation. Already used in some power plants, steam powered engines use gaseous water (steam) as the working fluid instead of carbon-based fuel [6]. This need for greater fuel efficiencies and cleaner fuel options are driving the transportation industry in new directions. The new direction could result in the resurgence of steam powered vehicles in the future. By out fitting a rotary steam engine to operate on superheated steam instead of fossil fuels, it would help reduce fuel consumption of nonrenewable resources and ultimately decreases harmful emissions. Certain advances in material technologymay make a modern steam engine feasible in today’s environmentally conscious society. Decreasing the size, while increasing the efficiency, and burning of cleaner fuels such as natural gas and bio-fuels could revolutionize the modern steam engine [7][8].To carry out a viability study of theSpinDyne rotary steam engine, analysis of the following subsections were undertaken: the rotary steam engine itself, the boiler/heat exchanger, the combustion and the condenser/pump.
In the past, the efficiency of the steam engine was limited by design type, manufacturing capabilities, available fuel, lubrication requirements, and limited knowledge of material science [9]. Some major concerns such as weight to power ratio, minimum component heat loss, and temperature and pressure ranges need to be addressed. One of the problems with earlier design was developing an engine case that behaved as an adiabatic component, without sacrificing the weight to power ratio that results from adding heavier insulation around the case. A more efficient thermal insulator such as aerogel [10] would be used.
A new approach will be introduced into our study whereby the engine would be treated as a universal component within which all other components will be governed. Temperature, pressure, and starting vane angle with corresponding cylindrical volume has been provided to us as an initial starting point for which other values will be derived. Assuming the engine is treated as an ideal isothermal and adiabatic system, a Matlab (Mathworks, Natick, MA) program will be used to calculate all other initial values such as specific volume, enthalpy, and entropy. With these values, using the laws of thermodynamics and the ideal gas law, a relationship between the initial volume and final volume of the fluid in the system can be used to calculate desired values at the final state. Finally, the end state computations can be used to calculate the required work, torque, and horsepower. However, these calculations will need to be adjusted due to the particular engine design. SpinDyne’s rotary steam engine operates on a two-cycle expansion process per revolution, meaning that steam is injected into the expansion chamber, expanded, and then exhausted four times per revolution [6]. This expansion allows for shaft power to be created.
Another problem with older steam engines was the need for oil pumps to deliver oil to the bearings without creating a need to separate the oil from the fluid. SpinDyne’s solution is to use oil-less lubricant capable of operating at very high temperatures with little to no metal-to- metal contact. Using gas foil bearings works ideally in this aspect [11]. All other moving components within the engine will be coated with a newly discovered material known as BAM (Boron-Aluminum Magnesium). BAM has an extremely hard surface with an almost frictionless characteristic that allows for a decrease in mechanical breakdown resulting from extended usage, to optimize engine performance [12]. This material is a key piece that will allow modern day steam engine to become reality.
This boiler/heat exchanger subcomponent of the steam generation cycle is the point where the system absorbs heat from the combustion process and begins the phase change from liquid water to steam. Previous research has shown that scaling on the heat exchanger tubes caused by accumulation of combustion materials will decrease boiler efficiency and tube life over long periods of time [13]. For this reason, the Lamont boiler will be used due to its’ vertical construction which allows for reduced scaling. This particular boiler system was selected due to its very high heat absorption rates, its relatively small size, and inexpensive and lightweight tubing [14]. Failure to prevent heat loss in the boiler was a problem with older steam systems. With improved knowledge in material science, heat loss in the boiler component can be reduced using the aerogel thermal insulator without sacrificing overall boiler structure and size [15].The incoming feed water is preheated using the exhaust gas exiting the boiler [16]. Increasing the temperature of the feed water reduces the amount of energy required to generate steam, and therefore, increasing the boiler efficiency. Once the steam is generated, before it gets to the engine to begin the expansion phase, it passes through a series of heat exchangers that continually heats the steam until the optimal superheated state is reached.
Currently, some power plants use steam as the working fluid instead of carbon-based fuels [6]. However, power plant usage of steam engines required a combustion chamber to produce the energy, or heat, needed to initiate the phase change from water into steam (the combustion chamber used carbon-based fuels to generate the required energy, thereby limiting the carbon emissions, not eliminating them) [6]. Research has been done on the combustion of fuels, which allows for a vast knowledge of fuel properties. The rotary steam engine plans to be powered by the combustion of a combination of different fuels simultaneously. The type of useable fuels are liquid propane, gas, biomass derived gases (BDG), and various other liquid or gaseous fuels. Each carbon-based fuel has a reaction that requires energy to initiate, termed the heat of reaction. Also, energy is released along with the products, termed heat of combustion. Most carbon-based fuels are exothermic and so if the energy released from the combustion is greater than the energy required to initiate combustion, than they are effective in generating positive net energy which comes out as heat. This heat will be used to generate steam.
Each gas has a different chemical makeup which allows specific fuels to burn hotter, faster, and longer [17]. This along with many other fuel properties will allow for a certain fuel or combination of fuels to be selected as the most efficient. A comprehensive Matlab program will be created and used to model the combustion process. This program will be designed to test the effectiveness of combined fuel versus a singular fuel to generate values of thermal energy input, flame temperature, and fuel to air ratios. This program can then be directly applied to the steam system allowing for instantaneous selection of the proper fuel. This type of optimization program has been previously created and used in industry for power generation. Not only will the programs decrease fuel consumption, which ultimately decreases overall cost, but will also reduce the carbon footprint of the system as a whole [18]. The program will allow for the best selection of fuel for the required need of the engine, thus improving the efficiency of the burner and the engine simultaneously.
No steam engine cycle works without a condenser. The second law of thermodynamics required all heat engines to reject heat in order to complete a full thermodynamic cycle. The condenser serves this purpose by behaving as a continuous cycle, allowing the steam rejected from the engine to be cooled and condensed before being pumped and re-introduced back to the boiler. The operating pressure should be as low as possible; having the condenser operate in a vacuum would be ideal, and would improve the thermal efficiency of the overall cycle [19]. The amount of heat rejected can be determined from the enthalpies of the steam entering and exiting the condenser [20].
The design of the condenser itself should accommodate the amount of heat that must flow out of it. Calculating the heat transfer coefficients, the convection from the steam, and the heat conduction through the condenser walls was used in certain Rankine cycle models to design earlier condensers [21]. This design should also be optimized by balancing the heat transfer surface area against the pressure drops caused by the larger area [22]. The use of special materials, like metal foam, can be used to increase heat transfer, at the cost of higher-pressure drops [23].
METHODS
Boiler/Heat Exchanger
Completed Method
The boiler converts incoming feed water to saturated steam. The super-heater further heats the saturated steam to the temperature required for use in the engine. Beginning with an ideal thermodynamic approach to the steam boiler and super-heater, modeled as a Rankine steam cycle, the thermodynamic state of the incoming feed-water was identified. Determining the water temperature (T) and pressure (P) allows for identifying the enthalpy (h), entropy (s) and specific volume (v) of the incoming feed water from thermodynamic tables. Assuming the boiler to be adiabatic with steady state flow and neglecting changes in kinetic and potential energy,and using the first law of thermodynamics for a control volume, determine the exit state of the saturated steam leaving the boiler was determined (1). Using the heat input from the burner and the first law equation, the exit enthalpy was also found as well as the exit temperature by assuming constant specific heat (Cp0) (2). Once exit temperature was known, the remaining thermodynamic properties were found from saturated steam tables. By knowing the desired temperature and pressure of the superheated steam for use in the engine, the amount of heat needed was determined by applying the first law.
Proposed Method
Once ideal conditions are known, determining a reasonable thermal efficiency of the boiler and superheater is next as well as using the calculated thermal efficiency to find the actual thermodynamic properties of the saturated and superheated steam.
Engine
Completed Method
Using various assumptions such as reversible adiabatic, negligible kinetic and potential energy, knowing initial thermodynamic state of the superheated steam entering the engine, and the volume of each process—intake, expansion, exhaust—a Matlab code was created to simulate the system (Prog.1). First, the steam entering the intake valve was modeled as a transient process with isobaric and isothermal conditions. With such a simple assumption state one was defined and all thermodynamic properties were obtained. As the valve closed the steam was allowed to expand in a fixed volume. Assuming that there was steady pressure variations and knowing the initial and final volume and the specific volume at each sub-state of expansion the mass can be found. A while loop was used to collect and store all thermodynamic properties using XSteam (Magnus Holmgren, within a vector and the pressure decreased and entropy stayed the same for each cycle. To end the while loop, state two and state one are used to compare error of mass and if the mass error is less than the user specified error the loop exits and state two is locked. As the now wet steam was allowed to exit through the exhaust, the transient process again was assumed to be isobaric and isothermal. This will lock in state three and now all thermodynamic properties were defined within the engine.
Once all properties were known the work of each process can be found. For the two transient processes of the intake and exhaust, the work can be found using the known pressure and volume difference for each given state. To find the work of the expansion process the sub-states are plotted on a Pressure vs. Specific Volume diagram and by finding the area under the curve was calculated using the trapezoidal rule (Fig.1). This area can be checked using the internal energy difference between states one, two, and multiplying the now known mass. Once all work can be found for each process and taking in account of the number of process happening per revolution, the power can be found by summing all the total work per revolution and multiplying by the design parameter for omega in revolution per second. This power can be converted to horsepower so it can be comparable to other engines. If the shaft angular velocity is known, then torque can be estimated. Finally, mass flow rate can be estimated using the total mass entering at each intake process per revolution and multiplying by omega.
Since the Matlab code was written as a function a second code was allowed to utilize it and vary parameters so horsepower and torque can be graphed and various other parameters tabulated for a range of conditions.
Combustion
Completed Method
A combination of fuels was combusted to create the energy that is used to power the rotary steam engine (Fig. 2). The first step of the combustion analysis process was to select which fuels were going to be used. The majority of the fuels selected were hydrocarbon-based fuels; however the engine will run on almost anything. The type of useable fuels are liquid propane, gas, kerosene, biomass derived gases (BDG), and various other liquid or gaseous fuels.