Supporting > Engine Ancillaries

IC Engine Water Pumps

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Rustkolector:
Charles,
I applaud your study and testing of small pumps designs for model engines. I have to agree with Roger B though that a brass gear pump solves most of small engine cooling issues. It is self priming and therefore provides flow at very low RPM’s and this feature also solves a lot of coolant piping issues. I have used the Jerry Howell designed gear pump design for single, twin, and 4 cylinder model engines with great dependability. Flow is determined by gear width and drive speed. It is reasonably easy to build with readily available spur gear stock and you can add a lip shaft seal. Drive can be direct or belt. 
Jeff

Charles Lamont:
An early test was to estimate the head needed give the required flow through the system. With fairly short hoses, a 100mm head was enough to give 0.3L/min with cold water and 0.4L/min with water at 48°C. The flow in the first case is laminar, and transitioning towards turbulent in the second, the water viscosity being so much lower at higher temperature.

The second picture shows the radiator and fan under test. There are temperature sensors at inlet and outlet, fed to an Arduino for display. With water entering at 71°C and exiting at 60°, an average of 50° above ambient, and a flow rate of 0.5L/min, the system was putting out almost 400W. Plenty.

Next, an overview of the pump test rig. It is admittedly rather rudimentary, but was initially intended for comparative rather than absolute measurements and the whole business is a sideshow anyway. The supply tank (stainless can) and collecting tub are obvious. The delivery tube outlet is set by ruler to a known height above the supply tank level mark. Depending on the height, the collecting tub is packed up to avoid spills. During a run, the water level in the supply tank is maintained as constant as possible by carefully refilling it from the big jug. After a timed run, the weight of water in the delivery tank is measure on the kitchen scales. The water temperature is noted from time to time, so the density can be used to convert the weight to volume of water. This is a much more accurate measurement than any means I have of measuring the water volume directly.

After a general closeup of the pump and motor, there is a shot showing the hall sensor pickup which is triggered by a magnet in the brass drive flange. This tacho signal is read by the Arduino and used to provide a PWM output to control the motor via a mosfet. The Arduino uses a PID (proportional, integral, and differential) algorithm to set the PWM output duty (proportion of the time that it is on). The four pushbuttons enable the speed to be set in 10s, 100s, & 1000s of rpm, and allow the gain values for each of the PID control parameters to be adjusted for stable speed control.     

To prepare for a run, the supply tank (stainless can) is filled to the mark, the head set by moving the hose up or down the vertical rod. The motor speed is set, and a quick run to get the speed control roughly stable. Switching off the motor means no more pulses, so the PWM duty stays somewhere near. After draining the collecting tub back into the supply tank, a run can be started. Switch on the motor and start the stopwatch (my phone). The fiddly bit is to use the big jug to maintain a constant level in the supply tank. When enough time or water has passed, switch off the motor and stop the clock.
Weigh the water and return it to the jug and dry the tub. Record all the readings for later analysis, and repeat. I generally set the head, and do a sequence of runs at different speeds. I find a reasonable run is either about three minutes before the jug holding arm protests, or, at higher flows, there is about 1300ml in the tub. 

Numerous potential refinements are not difficult to think of, but I do get pretty consistent results. 

Charles Lamont:
Mike, glad to be of service.

Roger, Jeff - I wanted to play with centrifugal pumps to see if I couldn't make one that would do the job. After all that is what full size engines have, and the challenge being the attraction. I agree with what you say about gear pumps, and have all-along regarded that as an easy way out backup solution.

Charles 

Zephyrin:
wow, thanks to share all these experiments, many skills throughout the posts for the design of a pump of your "seagull" , lucky engine !

ps
BTW, the big brother of the seagull, the seal engine, do have a centrifugal pump running at camshaft speed.

Vixen:
Hello Charles,

I have found the size and power of the radiator fan also has a great effect on the cooling system efficiency. A bigger radiator or a more powerful fan reduces the requirement on the water circulation pump. Also plain water is a better coolant than glycol antifreeze. But plain water causes more corrosion problems, so I generally use a mixed 50/50 solution of the two.

Mike

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