Water injection test for exhaust gas cooling

On Atex compliance Zone engines there are requirements for different parts, surfaces and fluids to meet certain temperatures. In this application and Atex zone, the required temperature for the exhaust gas is 200 Celsius and although this engine (at 160hp) meets the requirement with a maximum gas temperature of 192 Celsius but that was deemed to be too close to the limit.

Many alterations have been made to the existing cooler design to attempt bring the temperature down along with a few different configurations. All with varying degrees of success.

At this point my suggestion for some water injection to further cool the exhaust gases was accepted for an experiment. After some simple calculations with the nozzles that I could choose from the amount of energy taken from the exhaust gasses could be anywhere between 2 and 50kJ, assuming the water temperature is 93 Celsius (top hose temperature)  and that all the injected water is converted to steam (but then no more heating is done).

As the suppliers of the misting nozzles didn't reply to me with costings I made one instead. Making a nozzle (Fig 1 and 2) integrated into the system it was found that there was not a spray pattern but more of a jet (a second hole shown as the drill bit snapped in the first one), in order to rectify this some wire was soldered onto the blanking plate to help vaporise the jet (Fig 3 and 4), this worked surprisingly well for to the point that it was desired in the first place.

Fig 1 - Nozzle with a hole shown.

Fig. 2 - Nozzle jet at 0.5 bar.

Fig 3 - 'Vaporisation' wire after 1 run up.

Fig 4 -  0.5 bar past the vaporisation wire.

In order to do the test I wanted the engine to get up to temperature for the exhaust gas and then start the water injection process to show the difference in the temperature. In Figures 5 to 8 you can see the installation in the system

Fig 5 - Injector screwed into the cooler blanking cap.

Fig 6 - Whole cooler with the blanking plate attached.

Fig 7 - Tank mainly filled ready to be hooked up to the airline.

Fig 8 - Whole engine all wired up for various testing.

In Figure 9 you can see the trace for the test that was carried out. After the second start up when the exhaust gas temperature reached ~195 Celsius the system was plugged in. Initially this was run at 1.5 bar (then shortly thereafter reduced to 1 bar) and saw the gas temperature reduced to around 50 Celcius, unfortunately this is a false reading as it is 'over cooling' by pouring water onto the temperature sensors and not necessarily a true reading of the temperature.

Then the pressure was dropped which saw the temperature rise back up again. Then the injection was resumed at 0.5 bar leading to a gas temperature of ~130 Celsius with fluctuations due to the pressure regulator and other users on the gas lines. This is a more realistic reading with the amount of water that is entering the system. Once shut off again the temperature can be seen to rise again, showing that the system was actually making a difference to the gas temperature.

Fig 9 - Temperature traces for the test.

Bonus picture in Fig 10, what happens when you leave the airline plugged in and take the tank up to 3x its working pressure (4.5bar), by accident, but there was a very large bang and thankfully it was outside at the time and no one was hurt.

Fig 10 - Bonus picture!

Homebred 29 - Final checks before material purchase.

This should be the last post about design, everything after this should be about production, scary!

The jig is ready, the flux, brass, dropouts, BB, chainstays, bottle boss mounts and cable guides have all arrived from various parts of the world (Ceeway and Paragon).

To make absolute sure that everything is going to fit with no issues I have gone, what has been called, overboard in terms of checking clearances (and I admit they are very extreme). Unfortunately, although brazing is classed as semi-permanent in most frame builders books, once built up there is very little that can be done to rectify any geometry and clearance issues, unlike my carbon colleague Oliver (link to projects) who is able to saw large amounts of frame off and re-mould it. This isn't an option for me.

Front Wheel

I used a 2.6" tyre to check for clearance at the bottom of its travel (the ATC + the stack height of the bottom bearing) and then to the whole length of its 100mm travel to make sure that nothing would clash. This is also taking into account the fork offset used on the forks I intend to buy (44mm offset)

Fig. 1

Crown

This clearance between the crown at full rotation shows the fork crown to clear nicely with 2mm to spare. This is highly dependant on an arbitrary number I chose for the fillet radius on the crown so the down tube may be moved to provide a bit extra clearance in case of misalignment.

Fig. 2

Rear wheel on the chain stays

 Using a 2.55" tyre gives some clearance more typically seen on American designed frames. I will be running a 2.25" tyre instead giving enough clearance for the English weather.

Fig. 3

Rear Disc

A 180mm disc is by far the largest I will ever be using on the rear wheel so I have used that for clearances, it clears on both the chain stay and the seat stay.

Fig. 4

Fig. 5

Chainrings

Using measurements found for a variety of Shimano cranks the extremes of the dimensions were chosen. Along with the chosen dimensions of chain line from a mixture of double and triple cranks the measurements from a hope 34t chainring was taken and then scaled up to produce a 46t chainring in the out most position and a 36t chainring on the middle ring position, neither showed to be a problem.

The distances between the chainrings were measured from a set of FSA Afterburner triple cranks that I own.

Fig. 6

Fig. 7

The thickness of the chainrings is greatly exaggerated at the overall diameter so the clearance in reality will be far greater.

Cranks

Using the narrowest Q factor on a Shimano crank, that I could find actual measurements for, I produced the crank circulation for a 175mm crank with a a large amount of material after where the pedal would thread in to be sure. Again showing now issues.

Fig. 8

Heel and Toe

Using my EU48 Shimano shoes to produce very large blocks in the assembly to check the clearances a minor issue of heel rub on the chainstays was found. Considering the blocks used have sharp edges this will not be an issue but is still shown below. The toe clearance will be greater than shown for the reason previously stated.

Fig. 9

Fig. 10

Hopefully this will be enough to make sure there are no clashes and that I don't need to make any modifications to allow a usable frame.

In terms of calculations for the survival of the frame none have been done up to this point. I have decided up to this point that blissful ignorance is better due to the fact that I am buying the thickest gauge tubes I can from Reynolds. Fortunately to back up my expectations of my frames survival due to the heavy gauge, large diameter air hardened steel tubing, Stanton have released a new bike called the Sherpa (as seen on single track) which is using the same DZB (double zone butted) tubing that I am in the same steel alloy for the down tube. The down tube is the area I am most concerned about thanks to the angle it is sat at to the head tube and the forces I intend to put through the head tube, hence why my Surly Karate Monkey has extra bracing under the down tube (and why Reynolds have produced their DZB tubes). 

The chainstays I am using are from Columbus and come pre-bent, saving me a lot of issues with foundry sand, lead alloys or ice trying to bend the stays into some sort of usable shape. They are similar to the ones used in a Chickens frame designed for riding a cyclocross bike down sets of steps, meaning I have no great worries on these either.

As well as the clearances being checked some small geometry changes have been made so that I do not have to run my saddle at the extremes of what it was designed for. In order to do this the effective top tube has now been lengthened from 599mm to 630mm.

Displacer Valve test rig.

One of my projects at Power Torque Engineering this easter was to design and build a test rig for the new displacer valves. They have been designed (the displacer valves) by another engineer at the company and they work fantastically, however they are assembled in house and this assembly may damage the seals or internal workings. As the valves are going to be put straight onto an engine they need to be purged of air and replaced with oil and then pressure tested up to 10 bar (whereas the engine will reach 7 bar maximum).

The valve also has to be able to be changed quickly to allow for a quick turn around, so no threaded elements.

What I was given was a clutch master cylinder, a displacer valve, some material and a catalogue of components, along with plenty of help from the engineers there as this is my first hydraulic project.

Fig 1. The complete rig, now attached to the bench with G clamps.

As you can see, aluminium profiles are now my favourite system for test rigs. A toggle clamp with a two nylon cones are used to provide the seal. The clamp can hold up to 2kN in the current configuration (as the clamping point can move) and has been taken past the maximum reading on the pressure gauge with no leaking or bursts.

Fig 2. Close up of the nylon cone.

The nylon cone is the standard 60deg cone with a 2mm hold through to the 3/8" BSPT to allow the oil to flow. There is also a M6 thread in the back to allow for adjustment in the oil drip tray.

Fig 3. The plug for the back of the clutch cylinder

Using the insert as supplied by Ford a metal replacement was then created with a 3/8" BSPT at the rear and two flats to help with tightening when attaching the 3/8" BSPT to 1/4" BSPP.

Fig 4. Handle Clamp for converting to the master cylinder.

The clamp was machined as one although is two parts, swivels perfectly and is threaded in one of the blocks and has a clearance hole in the other, allowing for plenty of clamping surface. Also allows the swivelling  around the clutch cylinder.

Fig 5. The ball valve and pressure gauge.

Using a P clip the female-T was clamped easily onto the profile. The same goes with the ball valve, the holes were opened up to clear a M6 bolt and then threaded into the aluminium profile, providing plenty of security and strength for turning it.

Unfortuantely as the clutch cylinder was designed for DOT fluid and not 15W40 (JCB engine oil) the one way valve has swollen and will no longer allow fluid to pass in either direction, rendering the jig useless. Another pump is being sourced and is to be attached to the jig which will solve all the problems. Seen as all the hard work and plumbing is done, the only thing to do is clamp the new pump on and then plumb it in.

And that is the end of my jigtastic easter.

Bike frame jig complete!

This easter has been jigtastic at work with another jig been produced during work hours and this jig produced in lunch times or in the friday afternoons that are always given off.

The jig was designed in solidworks and uses 6x1m aluminium 40mmx40mm profiles from a profile distributor (valuframe in this instance) including 4 angle kits (seen in Fig. 2) and 4 90 degree angle kits.

Fig. 1 - Complete jig

Fig. 2 - The flexible angle kit used

The tapered holders (which were chosen over steps so an infinite amount of tube diameters could be used) seen in Fig. 3, Fig. 4 and Fig. 5 were made from 2.5" aluminium bar that was machined on a lathe at a 50 degree angle to the central axis, then 3 of the four cones were threaded with an M8 thread to allow them to be attached to the angle kits (which also had to be opened up on the milling machine as I was unaware they were supplied for M6 bolts). The bottom bracket tapered holder has a 8.25mm hole through to allow the threaded bar to clear, two nuts are then tightened onto each other to allow a bottom bracket to be attached of varying widths.

Fig. 3 - Head tube tapered holders

Fig. 4 - Seat tube tapered holder

Fig. 5 - Bottom bracket tapered holder

The drop outs have a slot all the way through of 8mm to allow the M8 bolts to go through. This allows for a lot of alignment to be considered if anything doesn't quite go so well. The cones on either end are to centre the drop outs of varying sizes (which should happen with various iterators) which have a 8.25mm

Fig. 6 - Drop out holder with cones.

And there you have it, I have completed the frame jig in approximately 10 hours work in a work shop. All ready for the summer to carry on with the rest of the build.

36" wheels, are dual discs necessary?

After a thread on singletrackworld where I asked if anyone had seen such a device for dual discs. It was recommended that I use a 4 pot hydro brake system with a very large rotor that is either from a tandem or custom laser cut (which I am uncomfortable with without a large amount of calculations). The single disc also proves potential problems with weird reaction torques through the hub shell (to the spoke flanges), only applying torque to one stanchion therefore making it fatigue sooner and the reaction from the axle (if a quick release is used) could eject the wheel from the forks. All of this is seems to me like a pretty bad idea for something that could be going up to 50mph.

The solution (in my mind anyway) is using two discs with one on the left hand stanchion in the standard orientation and then one on the right hand stanchion on the front as seen on Cotics road hog forks then this would have no reaction forces going through the axle so a QR could be used if required (although unlikely as stiffness will dictate a through axle should be used), would put near equal forces on the stanchions and there would be no torque through the hub shell.

So it would seem that dual discs were a good idea in these respects but in terms of stopping power (if you read the thread) it was questioned if it was really necessary in terms of stopping power, I tried to reason that it was as the energy of the rotating mass is larger on a 36" wheel and all the mass is further away from the centre, so requires a lot more torque. There were many nay sayers including Ben Cooper (a custom frame builder with a large number of interesting projects under his belt) so I thought I must have been wrong, so I did some calculations (outcome of 36" and 26" energy comparison seen below). After these calculations it was found that for a 180mm rotor on a 26" wheel I needed a 240mm rotor on a 36" wheel (or 2x120mm rotors in this case) but after talking it over with a few people I decided that dual 180mm discs were the way to go. You can see the force required at the tyre contact patch to deccelerate a 26" and a 36" wheel along with the force at the contact patch with dual 180mm rotors on a 36" wheel.

Kinetic energy against velocity, assumptions made of wheels taken to be hoops with all the weight taken at the rim bed.

Force at the contact patch, assumptions of no slip, front wheel only braking.

Weirdly it didn't make as much of a difference as I had expected on the energy front (about 5% greater over most speeds) but seen as there are other large benefits as listed above its going to be carried on with.

Unfortunately for me there has only been one dual disc system made and its about as rare as hens teeth so buying used is out of the question. Buying new is also out of the question as no one has a desire to make such a system due to the current systems being so good.

For the actual braking system the assembly will be pretty easy, two shimano SLX calipers will be used with a Zee lever which is designed for a 4 pot caliper so the stoke should move enough to provide ample pad/disc clearance and as they are easy to bleed it should be a simple process.

Strangely no one makes a dual disc hub, so I set about to design one using hope end caps and a hope bearing kit for easy rebuilds and spares sourcing. The spoke flanges had to be designed to fit the only rim available in the world, which is 36H and I did want to build it 4 cross but I would have to custom cut my own spokes (the wheel build comes out at ~£800 for this) and that means I would have to have a 3 cross build (which comes out a lot less money!). So this no longer has any bearing on the hub. The drawing for the hub can be seen below. Although the flange thickness's will probably change along with a few of the key dimensions.

So are dual discs nessacery? Yes, just because.

The 36" project

Ever after seeing this video I have wondered what it what it would be like to ride a 36er and how cool it would be to try it.

Now that orders are starting to be placed for my other project (the homebrew 29er) I thought I would spend some of my spare time trying to design one of these ridiculous monstrosities and then (depending on how the homebrew goes) make one.

Unfortunately due to the unusual size of the wheels the geometry actually has to be worked out instead of cherry picked from everyone else who knows what they are doing.

The aims are ultra short chain stays (to reduce the wheelbase), no toe overlap, low mechanical trail (~55-60mm to keep it sensible), potential for dual disc (for heat dissipation and stopping power, justified in another post) and with any luck fitted geometry! Hopefully this will keep it relatively well handling with a not unreasonable spread on the spokes to help keep some lateral wheel stiffness.

Acrylic compressed air engine

This project is from way back in April 2011 when I was watching plenty of videos on compressed air engines as part of some research work into a potential A-level project (which was later settled on an engine mount).

The below video is what got me  interested in trying to make one myself, so I set about designing one on CAD and making it out of acrylic.

The premise from the video is very simple, the cam allows the air to pass into alternate chambers and that turns the flywheel which then in turn takes it over the edge and into the next phase.

Thankfully it was very easy to design and the premise was simple, get the panels cut out and epoxy it together then spray a lot of air in there and hope for the best.

After using the facilities at the school to cut the acrylic out it was quite easy to slot it all together then use acrylic to make it air tight.

After it was all bolted down to a rather shoddy piece of MDF it was hooked up to an air compressor and it ran for a small amount of time. Nothing powerful, as mentioned in the video there is plenty of leakage between the chambers and my system of attaching it all together had a lot of slack, but it still ran. Below is the video of it running, filmed by a friend (also plays the roll of the starter motor) in the DT department.