Smart Engine User Manual
Contents
1. 2007 American Stirling Company Smart Engine User Manual as y To Lab Power Supply 12 V 3 A Power 9V DC Water Box and Engine The white plastic box can be filled with water and or ice in order to minimize the temperature on the cold side of the engine You can use the large clear plastic tubes to fill the box with water and to drain the box Use the supplied pinch clamps to keep the water in the box or drain it as needed The engine is mounted to the side of the water box and should need no adjustment 2007 American Stirling Company Introduction 7 Power Heating Resistors Tower The tower supports the tachometer sensor at the bottom the the power output and crankshaft of the engine and the spring scale for use in measuring power The large hole in the base just in front of the tower is used for measuring engine power Electronics The electronics are self contained and should not need adjusting 2007 American Stirling Company Smart Engine User Manual 1 3 Installation DAQ Software Insert the MCC DAQ Software CD into the CD DVD drive in your Windows computer The installation setup software should start up automatically You will not need either of the other CDs delivered with the DAQ hardware the UL for LabView CD or the Universal Library CD Install all of the software available on the MCC DAQ Software CD and then r2. The Smart Stirling Engines manufactured in the spring of 2007 include new hardware and software features not available in previous versions of this product Acquired data is now sent to the computer over a USB cable rather than over a serial cable which is much more in keeping with today s computers Data acquisition and analysis software has been written from scratch and includes many new built in features including e automatic generation display and evaluation of pressure volume P V graphs automatic computation of indicated power using the P V graphs e a built in software dynamometer computing power and torque using the rate at which the engine spins up the flywheel ability to save acquired data both for later re display and analysis as well as for transfer to Excel and ability to compute figures of merit power RPM etc for a series of experiments and send the summary to Excel We are proud of the new features which we are providing for you but also realize that the new software is not as thoroughly field tested as was the older software Please feel free to contact the author of the software directly if you have questions problems comments or suggestions Jon Bondy may be reached at jon jonbondy com 1 1 Packing List Your Smart Stirling Engine consists of the following the engine proper aplastic bag containing the software for the Data Acquisition System DAQ the Smart Engine Data Logger Software
3. ase ARARA aa Tae 90 95 100 105 110 115 120 125 130 135 Time milliseconds You can enable or disable any of the five graphs by clicking on the appropriate check boxes in the Enable Graphs panel You might choose to do this if you wanted to inspect one of the graphs in detail Typically three of the graphs are visible when you do a Grab and a different three graphs are visible when use the Dyna function Grabbing Data When you click the Grab button you acquire data from the engine for 1 second at 1000 samples per second The acquired Pressure data is graphed at the top and should appear as a sinusoid The Tachometer signal is also acquired and graphed below the Pressure data The Tachometer data looks like a single pulse for each rotation of the engine drive shaft with the pulse occurring when the piston is at the bottom of its stroke when the engine volume is at a minimum and pressure at a maximum The current temperature of the engine s left cold plate is displayed in the grid below the buttons as Lo Tmp the right hot plate temperature is displayed as Hi Tmp the power consumed by the four 1 ohm heating resistors is displayed as Res Pwr and the difference between the highest and lowest 2007 American Stirling Company Software Operation 13 pressures is displayed as Press When the engine is running very slowly sometimes only one pulse appears on the Tachometer graph When this happens the s
4. CD a plastic bag containing the USB cable a 9 V power brick an adaptaplug to connect the power brick to the engine electronics and this manual NOOR ND 2007 American Stirling Company 4 Smart Engine User Manual 1 2 Engine Nomenclature The Smart Engine consists of the following major parts 1 Front Panel 2 Water Box and Engine 3 Tower 4 Electronics Note that the 12 V 3 A power supply shown in the picture above is there for purposes of illustration only You must provide such a power supply yourself it does not come with the engine 2007 American Stirling Company Introduction 5 Pressure Sensor Helium Line Pinch Clamps Front Panel The Front Panel contains the followings indicators and connections 1 Helium Ports connect a helium supply hose here to flush the air out of the engine and fill it with helium to demonstrate increased performance with that gas 9 V DC Power Connection connect the supplied 9V power brick to supply power to run the electronics associated with the engine Power on LED which lights up when the 9V power supply is connected Lab Power Supply Connection connect your 12 V 3 A power supply here to power the high power resistors that are used to heat the hot plate of the engine USB Connection connect the engine electronics to your computer so that you can collect data from the engine a FO NW
5. CD supplied by American Stirling Company called Smart Engine Data Logger Software into your computer s CD DVD drive and install that software on your computer by executing SmartStirlingEngineSetup exe 2 Engine Operation The basic procedure for running the engine and taking data is as follows 2007 American Stirling Company Smart Engine User Manual 1 You may wish to fill the white plastic water box with an ice water mix to within one inch 2 5 cm of the top An ice bath is not required however maximum speed and power is only achieved with an ice bath to get the cold plate of the engine to be as cold as possible Make sure that the drain pinch clamp is closed tightly before you put water in the box 2 Plug the supplied 9 V power brick into the 9 V connector to provide power to the on board electronics The front panel LED should light up and the temperature display should show a temperature reading 3 Connect a USB cable from the engine to your Windows PC Start the Smart Engine Data Logger software Among other things this software monitors the temperature of the hot plate to ensure that you do not allow the plate to get too hot You should always run the Smart Engine Data Logger software whenever the heating resistors are powered up 4 Verify that your variable voltage DC power supply is turned off and then connect the wires from the DC power supply to the red and black binding posts on the lower right p
6. Smart Engine User Manual 2007 American Stirling Company 2 Smart Engine User Manual Table of Contents Part Introduction T Packing List sine 2 Engine Nomenclature 3 Installation 5 55 ia Part Il Engine Operation Part Ill Software Operation Part IV Pre Lab Part V Measuring Power Manually Part VI Troubleshooting 2007 American Stirling Company Introduction 3 1 Introduction Congratulations on your purchase of American Stirling Company s Smart Stirling Engine The Smart Stirling Engine is intended for engineering physics and thermodynamics classes at either the advanced high school or university level The engine is electrically heated for accurate power input measurements which also keeps fumes out of the lab and is cooled by air or water It has built in pressure temperature and angular position sensors and a data acquisition system to allow sensed data to be sent to a Windows PC where it can be plotted and analyzed A variable voltage DC power supply is available as an option if your lab needs one to power the electrical heating elements Stirling engines are heat engines that make exceptionally good teaching tools Not only does the Stirling Cycle match the Carnot cycle for efficiency but also real Stirling engines can be made to run on low temperature differences This ability to run on low temperature differences makes them well suited for use in laboratories
7. Sometimes you can find a leak by connecting a tube to one of the helium ports opening the associated pinch valve and blowing air into the engine leaks can sometimes be detected by putting a wetted finger near the engine or by using a small feather 2007 American Stirling Company
8. a are computed and graphed in the final graph at the bottom Press RPM and Ind Pwr will remain blank after you press the Dyna button 2007 American Stirling Company 14 Smart Engine User Manual Smart Engine Data Logger __Greb_ E Tachometer IF Continuous Dyna Export Multiple Help Quit 2 000 2 500 3 000 3 500 4 000 4 500 Time milliseconds 325K HiTmp 360 4K Res Pwr 34 6 W Pressure RPM Ind Pwr Power 10 87 mw Torque 0 18 mNm Instantaneous RPM Angular Velocity 7 Enable Graphs 2500 3 000 D Pressure Time milliseconds Power and Torque Data M Power Mass Diam MOI 120 0 0252 21 25 0 00164 14 25 0 00109 26 15 0 000073 5 6 32 7 168E 00 2 000 2 500 3 000 3 500 4 000 Time milliseconds Power milli watts oO To correctly use the Dynamometer facility you need to first get the engine up to some test temperature Slow the power output shaft down with your fingers until the engine is just barely running With the mouse hovering over the Dyna button release the drive shaft and then click the Dyna button The software will acquire data during the period when the engine is spinning the flywheel up to speed Power and Torque are computed based on how quickly the engine can increase the RPM and on the moment of inertia of the flywheel The grid at the lower left allows you to enter the masses in grams and diameters in mm of the various components of the cranksha
9. boss who doesn t have a clue about physics is demanding that you make the Smart Stirling Engine more efficient or else he s going to take away your company car and cancel your expense account Your boss does understand expense accounts So if the Carnot formula determines the maximum efficiency of any heat engine and we know that we can t exceed this then the question comes to mind how much of the Carnot efficiency can we reasonably expect to achieve with any given engine Well if you have been extremely careful and if you use the right type of engine a Stirling engine you can get up to 50 of Carnot efficiency Perhaps this could be achieved with other cycles as well Any heat engine that achieve 50 of Carnot is an extremely efficient engine 2007 American Stirling Company Pre Lab 17 With all this talk about efficiency and the fact that Stirling engines have the most efficient engine cycle possible you probably wonder if the Smart Stirling Engine is a 50 of Carnot engine Not a chance Is it a 25 of Carnot engine No Then why do we have one in the lab We have one here for several reasons First it is a good teaching tool to help you learn about engines in general This engine wasn t designed to be efficient It was designed to be a good teaching tool to work well in a lab and to be easy to understand It was also designed to a specific price because if a school can t afford to buy one it doesn t do an
10. display like the following Smart Engine Data Logger Grab i Pressure kPa IF Continuous Dyna Export Multiple Help Quit 400 500 600 Time milliseconds 307 6K HiTmp 360 4K Res Pwr 34 6 W Press 3 03 kPa RPM 869 6 Ind Pwr 45 4 mw Power Torque Enable Graphs 500 M Pressure Time milliseconds M Tach lv PA Pressure vs Volume RPM Power Mass Diam MOI Ea on 120 0 0252 25 0 00164 25 0 00109 15 0 000073 3 2 7 168E 00 Pressure Oo on L w Volume cu mm There are five main functions represented as buttons e Grab click this to acquire 1 second of data and view the Pressure Tachometer and PV graphs Dyna click this to acquire 5 seconds of data and view the Tachometer RPM and Power Torque graphs Export click this to save your current data in a CSV file for later use by Excel or to re Import the data back into this program Import click this to re load data which you saved previously The software comes pre loaded with various input files which you can load and inspect Multiple clicking this allows you to load a series of import files compute their figures of merit RPM power etc and create a single spreadsheet CSV file that contains a summary of all of this data This can be very helpful if you want to see RPM or power trends for differing engine temperatures The Help button summons this help information the Quit button terminates the program The Cont
11. e boot your computer InstaCal Software Your engine comes with the DAQ hardware the USB 1208LS a fist sized gray box mounted on the rear of the engine already installed Plug the provided USB cable to connect the engine with your computer Wait until the computer says that your new hardware is ready for use Using the Start button on Windows locate the Measurement Computing software that you just installed and start the InstaCal program When InstaCal notices the new 1208 hardware allow InstaCal to add the 1208 to the list of known devices Plug and Play Board Detection The following plug and play devices have been detected USB 1208LS serial 47 Check those devices you wish to have added to the configuration file Then under the Install menu use Configure to set the 1208 to single ended mode If you fail to do this the software will not function properly The original form should look like this 2007 American Stirling Company Introduction 9 Board Configuration USB 1208LS Factory Serial No 12738EB Custom Serial No 47 No of Channels E Differential Flash LED Firmware Version 1 00 Board Configuration USB 1208LS Factory SerialNo 12738EB Custom Serial No 47 No of Channels f Single Ended Flash LED Firmware Version 1 00 Smart Engine Data Logger Software Once the DAQ hardware and software are correctly installed insert the
12. e engine and stalls it It is acceptable to unwind the string by gently pulling on it and reversing the direction of the engine as it unwinds Vary the weight used from one so light that the engine hardly slows down to one so heavy that it almost stalls the engine and takes quite a while to raise the weight Set the engine up at a given hot and cold temperature start it running and lift one of your weights and time how long it takes to lift the weight Then proceed to the next of your weights collecting a series of weight time data pairs Then use the following formulas to compute power for each of the weights you used You should collect 10 20 data points using different weights In this case power is mass gravity height raised elapsed time We have prepared an Excel spreadsheet to help you perform these computations easily Computing Power by Lifting Weights xls 2007 American Stirling Company 18 Smart Engine User Manual Measuring Power with a String Brake Tie a thread to the spring scale drop it down to the power output shaft and and wrap it three times around the shaft so the spinning shaft wants to lift the weight as shown Then drop the weight down through the hole and hang your weights at the end of the string Set the engine up at a given hot and cold temperature start it running and hang one of your weights at the end of the string so that it is hanging in the air Measure the RPM of th
13. e engine using the Grab feature in the software and record the RPM as well as the mass of the weight and the reading from the spring scale Then proceed to the next of your weights collecting a series of weight spring scale reading RPM data triples Then use the following formulas to compute power for each of the weights you used You should collect 10 20 data points using different weights This approach is a good method for measuring power you have just built a simple prony brake It is quite easy to use although not as emotionally satisfying as watching the weight being raised from the floor Torque W S A R 2007 American Stirling Company Measuring Power Manually 19 where W mass of weight in kg S spring scale reading in kg A acceleration of gravity 9 8 m sec R shaft radius in meters 0 0016 Power T engine radians per sec where T Torque engine radians per sec RPM 2 pi 60 We have prepared an Excel spreadsheet to help you perform these computations easily Computing Power Using a String Brake xls 6 Troubleshooting Air leaks If you suspect that your engine might be leaking spin the drive shaft with your fingers while Grabbing some data The pressure should be greater than 3 kPa peak to peak If it is closer to 2 kPa then you probably do have a leak Attempt to isolate and repair the leak using the above test as an indicator of when you have fixed the leak
14. ft and the flywheel The values shown in the screen shot above are for in order the plastic flywheel the large brass disk the full diameter portion of the smaller brass disk the small diameter portion of the smaller brass disk the hub of the plastic flywheel and the steel drive shaft The moments of inertia are computed using formulas for solid disks cylinders The values shown are 1000 times the computed values in kg and m so that they can be read reasonably The Power and Torque graphs have both thin dotted lines and thick lines the former are the raw data while the latter are smoothed data averaged over more than one value of the raw data In theory the Power and Torque that are computed in the Dynamometer function are both accurate and calibrated as is the Indicated Power that is computed using the PV approach when you Grab data In addition Indicated Power is the maximum theoretical power of the engine ignoring power that is subsequently lost due to friction or other losses That is one would expect the Indicated Power to always be larger than the Power that is computed using the Dynamometer approach or the braking method described below Export 2007 American Stirling Company Software Operation 15 You can export your data either Grab or Dyna at any time by clicking the Export button Data is saved in CSV form for later import into the spreadsheet of your choice or for re Import into this prog
15. inuous check box allows you to perform Grab operations repeatedly if you want to watch the engine s performance change over time The numbers below the Quit button show the current hot and cold plate temperatures the numbers in 2007 American Stirling Company 12 Smart Engine User Manual the white grid show the data that has been acquired using Grab Dyna or Import The colored box to the right of the Grab button should be green at all times if it becomes red that indicates that the USB connection with the DAQ system on the Smart Engine has stopped working correctly The Graphs All of the graphs are automatically scaled to fit as much data as possible on the graphs If you want to look at the details of some part of a graph position your cursor at the upper left corner of the data you wish to inspect press the left mouse button down drag the mouse to the lower right corner of the data and then release the mouse The graphs will zoom to show you the data you selected To view the entire graph again click and drag in the opposite direction from the lower right to the upper left You can also pan the graphs whether zoomed or not by dragging the graph with the right mouse button Here is an example of zoomed Pressure and Tachometer graphs Pressure kPa 90 95 100 105 110 ans 120 125 130 135 Time milliseconds Tachometer SE annee s E E EA A E O A A AO E a less TIT EEEE a E E peta E R e E E
16. lly is By the time this lab is over you should have a much better intuitive understanding of these things and of engines in general We ll start with a few questions 1 What s the difference between watts and horsepower 2 Can you convert between watts and horsepower 2007 American Stirling Company 16 Smart Engine User Manual 3 If so then what is the conversion factor 4 Is the watt an acceptable way to measure mechanical power as opposed to electrical power 5 If process A is 50 efficient and it feeds into process B which is also 50 efficient what is the overall efficiency of A feeding into B and becoming a useful output at C 6 True or false the correct way to obtain efficiency for a system is to average all the various efficiencies that make up the system 7 True or False If a process is inefficient it is therefore a bad process 8 Could an inefficient process ever be a good process 9 What circumstances can you think of that might make an inefficient process a good one 10 Calculate the Carnot efficiency of a heat engine with the hot end at 100 C and the cold end at 23 C and also with the cold end at 0 C Discussion The engine that we are going to work with in the lab the Smart Stirling Engine is called a Stirling engine It was invented in 1816 by a Scottish minister named Robert Stirling who didn t name it after himself He called his engine a hot air engine with an economise
17. oftware is unable to determine the speed at which the engine is running and the RPM and Indicated Power values cannot be computed and will not be displayed If the engine is running quickly enough more than one Tachometer pulse is acquired and both RPM and Indicated Power is computed and displayed in the grid below the buttons as RPM and Ind Pwr When you Grab data the Power and Torque values are always blank they are computed with the Dyna function RPM is computed by locating two adjacent Tachometer pulses computing the time that elapses between the pulses and computing the rotational speed from that time Indicated Power is computed by plotting a Pressure Volume graph PV graph and computing the area inside the enclosed line Pressure data acquired from the engine and plotted in the top graph is used directly to create the PV graph Volume data is not acquired directly from the engine but is inferred by assuming that the drive shaft is rotating at a constant speed and computing the engine volume over time as the piston moves in and out The area inside the curve is computed and multiplied by the engine RPM to produce a power value The Dynamometer When you click the Dyna button you acquire data from the engine for 5 seconds at 800 samples per second The acquired Tachometer data is plotted in the top graph The RPMs are computed for the entire 5 second period and are displayed below the Tachometer data Power and Torque dat
18. ortion of the front panel to provide power to the heating resistors 5 Adjust your power supply so it is supplying 12 volts at about 3 amps or about 35 watts After the power has been turned on it may take three to five minutes before the engine is hot enough to run since Stirling engines do not start instantly or automatically You can monitor the temperatures by inspecting the temperatures shown on the LCD display on the black electronics box at the left rear of the engine or by watching the pair of temperatures displayed under the Quit button by the Smart Engine Data Logger software When the engine has become hot enough generally a 20 C temperature difference gently spin the output shaft clockwise by hand to start the engine If the engine is hot enough it will start quickly and build up speed If the engine is not hot enough no amount of spinning will make it start Air leaks sometimes caused by pinch clamps that are not tight enough can also cause the engine to fail to start even when hot You should keep the engine running at all times while the engine is being heated if the engine stops running heat starts to build up on the hot plate and the engine may over heat If the hot plate on the engine gets too hot either turn the 12 V power supply off or lower the voltage and or current 6 While exact performance will differ with changing atmospheric conditions and the condition of your engine the Smart Engine needs a temperature diffe
19. r About a hundred years later someone else decided that these engines should be called Stirling engines and the name stuck When you read the history of science it always seems that theory comes first then someone figures out how to make something useful out of it But that s not the way it usually works For example the Stirling engine was invented by Robert Stirling in 1816 About fifty years later a very good French scientist and engineer named Sadi Carnot came along a figured out an extremely useful formula for determining just how efficient any given heat engine could be The formula is as follows Temperature of the hot side of the engine minus temperature of the cold side of the engine divided by the temperature of the hot side of the engine times 100 is the maximum efficiency possible for any engine operating between those temperature extremes The formula is written T hot T cold T hot It s important to remember to use absolute degrees such as Kelvin or Rankine If you plug Fahrenheit or Celsius degrees into the Carnot formula all you will get is a meaningless number So here s another question Say you have an engine operating between a T hot of 100 degrees C that would be 373 K and a cold reservoir of room temperature say about 22 degrees C or 295 K 11 Which will get you more efficiency according to Carnot raising the hot temperature 25 K or cooling the cold temperature 25 K Please take this seriously as your
20. ram Import You can import and re analyze any of the data that you previously saved using the Export button The graphs and figures of merit RPM power etc are re computed Multiple This button allows you to perform multiple Imports and to save a summary of the figures of merit in a summary spreadsheet You will first be asked where you wish to store the summary data Create an appropriate file name for the summary data You will then be asked to select multiple Import files for analysis Use lt Ctrl gt lt click gt to toggle which files you wish to include in your analysis When you have the correct list of files selected click Open and each file will be imported in turn and the computed values output to the summary CSV file The resulting file will look like this in your spreadsheet 4 B C D E E G 1 File Lo Temp HiTemp RPM Ind Pwr Power Torque 2 _3 E3 310KCSV 297 9 309 6 66 1 3 8 _4 E3 313K CSV 293 9 313 5 267 9 5 4 _5 E3 315K CSV 302 7 315 4 93 9 3 1 6 E3 315Ka CSV 302 7 315 4 84 29 _7 E3 316KCSV 298 8 316 4 170 3 4 _8 ES 321KCSV 298 8 321 3 301 5 6 1 _9 E3 330K CSV 300 8 329 1 535 7 10 8 _10 E3 335K CSV 302 7 335 631 6 11 9 11 E3 340K CSV 301 6 340 6 779 2 21 4 12 E3 350K CSY 305 7 350 6 662 4 24 6 13 E3 360K CSV 306 6 361 3 1052 6 34 5 14 E3 370K CSV 307 6 369 1 1111 1 47 5 4 Pre Lab Stirling Engine Pre Lab This lab is about practical stuff like power and energy and what efficiency rea
21. rence of approximately twenty degrees C to run when its working fluid is air and ten degrees C if helium is used as the working fluid Maximum performance is achieved with the hot side at the maximum allowable temperature of 370 K and the cold side at 273 K Note that if you exceed the maximum hot temperature of 370 K the engine may develop a leak and may stop working entirely monitor that temperature carefully while running the engine 7 This engine spins clockwise when you are looking at it from the front It is worth noting that you cannot harm the engine by spinning it backwards In fact if the engine is hot and is spun backwards it may come to a complete stop reverse itself and run in the clockwise direction Software Operation With your Smart Stirling Engine running and with the USB cable connecting the engine to your Windows computer run the Smart Engine Data Logger software If you see an error message like this verify that you performed the Installation correctly Smartenginedatalogger DAQ hardware not Found plug your USB cable in and re start this program You may have to run the InstaCal program again 2007 American Stirling Company Software Operation 11 If the green box to the right of the Grab button is red or if you do not see waveforms like the ones below verify that you performed the Installation correctly Once the connection with the DAQ hardware is working correctly you will see a
22. yone any good In the lab you will find out what it s real efficiency is compared to it s Carnot efficiency Now for the last prelab question 12 How much of the heat that is expended in heating these resistors actually goes into the Stirling engine as opposed to simply heating the air around the engine Here is a hint measure the area of the rectangular resistors How much of this area is in contact with the engine 5 Measuring Power Manually Measuring Power Manually Shaft output power can be measured manually in one of two ways 1 Raise a weight from floor level to the bottom of the engine and time how long this takes or 2 Suspend a thread from the spring scale and wrap it around the output shaft in such a way that the spinning output shaft wants to raise the weight and measure the resulting engine RPM Measuring Power by Lifting a Weight Place a measured weight in the range of 10g to 30g on the floor tie a thread to it and run the thread up through the access hole in front of the engine tower Place the weight directly below hole on the floor and allow roughly 30 cm of thread beyond that needed to reach the shaft Wind the thread around the spinning shaft until it catches and then carefully guide the thread onto the spinning shaft to make sure that it does not bind or fall off the end of the shaft Have someone measure the amount of time that it takes to raise the weight from the floor until the weight hits the bottom of th
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