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Testing Models

Testing of model steam engines and turbines.

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Turbine Guy19/06/2020 11:57:58
202 forum posts
116 photos

I ran the Tyne engine on steam with my Stuart Turner Twin Drum Boiler. This is my smallest boiler and was intended to be used with engines like the MSM Tyne or Stuart Turner ST oscillating cylinder engines. I thought I fixed the relief valve, but it leaked in this test preventing the pressure from getting to the 25 psig I planned to run at. After running long enough for the speed to stabilize at the lower pressure, I blocked the leakage out of the relief valve just long enough to get the pressure up to 25 psig and run at that pressure for a short time. The maximum speed obtained with the APC 15x10 propeller was approximately 700 rpm. The speed remained almost constant for all the time I had the 25 psig pressure. I updated the following chart to include this test. The Tyne was very easy to get running. It passed the slugs of water you get when first starting with steam and started running at a constant speed very quickly. The total time of the run was 8 minutes and 40 secs. It ran very smoothly for the entire length of the run. The displacement lubricator and steam oil provided by MSM appeared to give the piston and O-ring all the lubrication they needed. I oiled all the external joints needing lubrication with a light machine oil. The vibration of the Tyne engine was quite a bit less than the ST even though neither of these oscillators show any attempt to control vibration.

Oscillators Test Result 3

Turbine Guy02/07/2020 12:07:40
202 forum posts
116 photos

Deleted Post

 

Edited By Turbine Guy on 02/07/2020 12:21:31

Turbine Guy02/07/2020 12:57:41
202 forum posts
116 photos

The following table shows the maximum performance of my three steam engines running on air. It also includes the percent of the total available energy lost due to leakage for each of these engines. I wanted to point this out since it is the biggest loss for the simple oscillating cylinder engines and is significant for the more complex engines. I determined the amount of mass flow lost due to leakage by subtracting the mass flow required to fill the cylinder from the total mass flow going to the engine. The energy lost due to leakage is proportional to the amount of mass flow lost due to leakage divided by the total mass flow going to the engine.

Energy Loss due to leakage = (Total mass flow – Mass flow to fill cylinder)/ Total mass flow, %

The Tyne steam engine comes with almost all the improvements I made to the Stuart ST steam engine, plus a sealing gland on the piston rod. The one improvement I did better on the modified Stuart ST engine was the very tight clearance of the cylinder support shaft. The Tyne steam engine has tighter clearance on the cylinder support shaft than the original Stuart ST steam engine but not as tight as the modified Stuart ST steam engine. You can see from the table how important that clearance is.

My Steam Engines 1

Turbine Guy03/07/2020 15:22:29
202 forum posts
116 photos

To try to confirm that the most leakage of the oscillating steam engines was caused by the tilting of the cylinder, I measured the separation of the cylinder face from the standard. With the air pressure on, I rotated the propeller by hand and measured the maximum distance from the face of the cylinder to the face of the standard. The cylinder tilted away from the standard on the top side when the air was pushing on the bottom of the piston. The cylinder tilted away from the standard on the bottom side when the air was pushing on the top of the piston. I could see the tilting by shining a light on the side of the cylinder. I could only measure the separation on the top side because it was accessible to a feeler gauge. The maximum separation of the Tyne steam engine was 0.005” and stayed at that distance most of the time the port feeding the bottom side of the piston was open. I made a calculation for the leakage from the perimeter of the port assuming the average separation was 0.003”. The calculated mass flow was close to the loss found from testing. A loss of 65% of the available energy is so large that I tried to find an example of a way to eliminate the tilting. The following drawing was copied from E. T. Westbury’s article ‘The MUNCASTER steam-engine models’. This model supports both sides of the cylinder which could greatly reduce if not eliminate the tilting. This model is very sophisticated with many additional benefits but eliminates the simplicity that is the main virtue of the oscillating cylinder engines.

Muncaster OC

Turbine Guy06/07/2020 16:43:22
202 forum posts
116 photos

I measured the maximum separation of the cylinder face from the standard on my Stuart ST steam engine like I did with the Tyne steam engine. I couldn’t get my smallest feeler gauge into the gap, so the maximum separation is less than 0.002”. I could see that the faces were separating by shining a flashlight on the opposite side, but the gap was much smaller on the Stuart ST. Tightening up the clearance of the cylinder support rod has almost eliminated the tilting. This should have reduced the leakage mass flow much more than I found in the tests. I rotated the flywheel by hand with an air pressure of 22 psig and noticed the leakage from the gap between cylinder and standard faces was much lower than what was coming out of the exhaust. When I rocked the flywheel back and forth, the piston O-ring would seal again and the leakage through the exhaust port was reduced to a very small amount. When the leakage through the O-ring was almost stopped, the total leakage was very small. The floating O-ring concept that I am trying gets it’s name from the movement of the O-ring from one side of the O-ring groove to the other side each time the direction of the pressure changes. When working correctly, this movement reduces the friction and extends the life of the O-ring. I did these tests without adding any oil, so I added oil and did them again. With oil added, the O-ring moved across the groove and sealed the gap each time the direction of pressure on the piston changed. The floating O-ring worked when there was enough oil but not when most of the oil was gone. The oil is blow out of the cylinder fairly quickly when the engine is running, so the floating concept probably is not working with intermittent oiling.

Turbine Guy12/07/2020 14:37:57
202 forum posts
116 photos

I tried the floating O-ring concept when I added the O-ring to my Stuart ST oscillating cylinder engine because I was concerned that the friction added by the conventional O-ring would reduce the performance at low pressures. To compare the friction of the floating O-ring used on the Stuart ST to the conventional O-ring used on the MSM Tyne I needed to estimate the indicated power. The indicated power is the power produced by the steam engine without any mechanical losses due to friction or binding. It includes the gas pressure losses in filling and exhausting the cylinder. It also includes the losses due to compressing the gas if the exhaust port is closed before the end of travel of the piston. I need to have most of the engines dimensions to estimate the indicated power. I have a Stuart ST drawing giving me the dimensions for that engine. I don’t have a drawing for the dimensions of the MSM Tyne and have not taken this engine apart and measured the components. Since the two engines are almost identical, I assumed the clearance volumes, average port openings, and other key parameters would be close to the same value. The estimated indicated power shown in the following table is based on using the actual dimensions of the Stuart ST and Chiltern engines and assuming the key dimensions of the Tyne engine are the same as the Stuart ST. The mechanical efficiency of a steam engine is equal to the actual power output divided by the indicated power. Comparing the performance found from my testing of the MSM Tyne steam engine with the Stuart St engine seems to confirm that the mechanical efficiency is higher with the floating O-ring than with a conventional O-ring. My tests with packing indicated that the packing, after bedding in, performed about as well as the floating O-ring. I recently tried replacing the floating O-ring with Teflon packing. It showed promise of having even better performance than the floating O-ring, but I dropped the Stuart ST engine and damaged it before I could confirm this.

My Steam Engines 2

Turbine Guy24/07/2020 18:32:18
202 forum posts
116 photos

I put the piston packed with Teflon into my second Stuart ST steam engine. This engine did not have the standard and cylinder faces machined at the same time which was one of the biggest improvements on the other Stuart ST steam engine that was damaged. After several five minute long runs to bed in the packing, the top speed with the APC 15x10 propeller was a little over 850 rpm. The performance even without the machined faces was about the same as the MSM Tyne steam engine. Both of these engines have considerably lower efficiency than the Chiltern steam engine even though it costs less than either of them. The following picture shows the Stuart ST on the left, the Chiltern in the center, and the MSM Tyne on the right. You can see from the picture how much larger the Chiltern engine is. The advantage of the simple oscillating cylinder engines is that they can be made very small which is helpful for fitting into small model boats. The Chiltern engine would need to be used in a much larger model boat. The only non-oscillating steam engine in the size range of the Stuart ST and MSM Tyne engines I found is a Saito T-1. The Saito T-1 has a piston valve, is single acting, and uses close fits for sealing the piston and piston valve. There is no packing, piston rings, or O-rings used in this engine. I ordered a Saito T-1 engine and will see how it compares in performance to my other steam engines.

Steam Engines

Turbine Guy28/07/2020 14:37:52
202 forum posts
116 photos

I received the Saito T-1 steam engine and it is about the same size as the Stuart ST and MSM Tyne Steam engines as can be seen by the following photo. The instructions are written in Japanese, so I couldn’t get any information from them. I did find on the internet that the pressure relief valve on the Saito boiler recommended for this engine is set for 1.2 bar. There is also an instruction manual for the Saito S3R that is written in English available from the Saito website. The Saito S3R is a three cylinder version of the Saito T-1 engine. The instruction manual for the Saito S3R steam engine gives all the information needed for operating and should be applicable for the Saito T-1. I'll give the test results for the Saito T-1 steam engine in the next post.

Steam Engines 2

Turbine Guy29/07/2020 12:06:13
202 forum posts
116 photos

My first test runs of the Saito T-1 were with the APC 8x6 propeller that I thought would be best for this engine. I ran the Saito T-1 at different pressures up to 30 psig. I oiled the engine before each run with a new pressure and ran it long enough to obtain a maximum speed.  I then ran a series of tests with the APC 15x10 propeller doing the same thing. In all the first tests the airbrush compressor was cycling on and off. The Saito T-1 is designed to run at pressures around 1 bar or approximately 15 psig. Running the engine at that speed had my airbrush compressor cycling with the motor constantly turning off and on. Since the performance was best with the APC 8x6 propeller, I increased the pressure until the airbrush compressor was running continuously. The maximum pressure the airbrush compressor was able to reach with this engine was 35 psig. My tests with nozzles showed the mass flow was approximately 1.3 lbm/hr with the airbrush compressor running continuously at 35 psig. The following table shows the results of these tests. Running the pressure much higher than 15 psig will shorten the life and is not recommended. The performance at the pressures shown in the table illustrates what the engine is capable of. The Saito T-1 and the matching Saito boilers have been used in several small model boats as shown in videos on the internet. I will add the maximum performance of the Saito T-1 in the table showing the performance of my other steam engines in the next post.

Saito Test 1

Edited By Turbine Guy on 29/07/2020 12:11:48

Turbine Guy30/07/2020 15:15:53
202 forum posts
116 photos

Since the Saito T-1 steam engine uses most of the same parts as the Saito S3R steam engine, I checked on the Saito website what boiler was recommended for the S3R. The recommended boiler was the Saito BT-1L. The pressure relief valve for this boiler is set at approximately 2 kg/cm^2 (28.5 psig). This indicates that the Saito T-1 could be run at a pressure of 25 psig which is the typical design pressure of the oscillating cylinder steam engines. I looked at the exploded view from the Saito S3R instructions which showed the parts. The exploded view shown below is a copy of the portion showing the piston, cylinder, valve, and connecting rods. When I saw that the flow had to go through a hole in the piston valve, I was surprised that the Saito S3R could run as fast as it did in the testing. When I measured the parts necessary to estimate the indicated power, I found that the average opening area of the valve was approximately 0.0018 in^2. The average opening area of the Stuart ST steam engine is approximately 0.00084 in^2. Even though the Saito T-1 engine doesn’t take advantage of the larger average opening area that a slot in the piston valve would provide, it still has over twice the average opening area of the Stuart ST. This is because the hole in the piston is fully uncovered at one point of the piston valve travel. The maximum overlap of the ports in the Stuart ST steam engine is way below fully open as can be seen in the drawing shown on the post of 29/11/2019 in this thread. A significant advantage of using a hole in the piston instead of a slot, is the leakage area is much smaller.

Saito Exploded View

Turbine Guy07/08/2020 12:02:30
202 forum posts
116 photos

I ran my Saito T-1 on steam from my twin drum boiler. Because it is single acting, it took several turns of the APC 8x6 propeller before it would run. After running a short time, the speed increased until a top speed of 2,400 rpm was reached. It held approximately this speed for the remainder of the test. The relief valve was leaking a little at the start of the test so I couldn’t measure the mass flow to the engine. The relief valve stopped leaking and most of the test was with all the steam going to the engine. The test with my turbine 2 with this boiler and at approximately the same pressure of 25 psig had a mass flow of 1.3 lbm/hr. The displacement lubricator supplied with the engine appeared to work well. The lubricator only has a removable top and no removable part on the bottom to drain the water. The instructions only say to add oil and there was space for oil after the first test. I ran the Saito T-1 on air after the test with steam and it reached a speed of 2,300 rpm with a pressure of 25 psig. I added the results from these tests to those of the oscillating steam engines as shown below. Unlike the MSM Tyne engine, the Saito T-1 had slightly more power with steam than with air at the same 25 psig pressure.

Oscillators Test Result 4

Edited By Turbine Guy on 07/08/2020 12:04:41

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