fuel tank – Experimental Engineering

Posted on June 25, 2017 by The Engineer — Leave a comment

nb Tanya Louise – Oil Cooling Improvements

Since the engine & hydrostatic transmission were installed in the boat a few years back, the hydraulic oil cooler has been in the same fresh water circuit as the engine’s water cooling system, however this has been causing some heat issues with the engine & hydraulic system under a heavy load, such as when I’m using the onboard generator to run the welding gear. The hydraulic oil temp would rise to over 80°C during the course of a long day’s cruising – such temperatures will degrade the oil very quickly, and in turn will cause premature wear of the very expensive hydraulic pumps. (Not to mention increasing the requirement for hydraulic oil changes, which are very expensive). The engine oil has been cooled by a standard automotive oil radiator, with air forced over the matrix by two large fans. This is also pretty inefficient, so another cooler will be added to replace the automotive one.
This cooling requirement is caused by the inefficiency of hydraulic systems – a simple variable displacement piston pump driving a bent-axis piston motor has an overall efficiency of roughly 80%. Given our engine’s max power of 76HP (56.7kW), this gives an energy loss of 15.2HP (11.33kW) at maximum power. This extra heat overloaded the skin tank, resulting in a cooling system that didn’t really work all too well once the engine was hot.

To solve this issue, we’ve decided to run a raw water circuit using the canal to remove the waste heat from the hydraulic system & engine oil, putting less of a heat load on the skin tank to bring the temperatures down to something reasonable. The image above show the system at running temperature after I installed the monitoring instruments. The top gauge is measuring engine oil temperature, at the point where it’s being fed to the bearings. The bottom one is measuring hydraulic oil temperature.

The engine oil temperature does have to be higher than any other cooling circuit on board, to boil off any condensate from the cylinders. Overcooling the oil in the sump will eventually cause sludging as the oil tries to absorb the resulting water. I’m aiming for a system temperature in the engine oil circuit of 95°C-120°C when the engine is under load & at operating temperature.

Water from the canal is drawn from a skin fitting installed at the last drydock visit, pulling water through a strainer to remove all the large bits of muck. The large slotted screen on the suction skin fitting keeps larger objects out of the intake.

A flexible impeller pump provides the power to move water through the system, in this case about 25L/Min. This pump is a cheap copy of a Jabsco pump from eBay. So far it’s been pretty reliable.

The temperature senders are standard automotive parts, and some adaptors were required to graft them into the oil lines of both systems. The senser’s 1/8″ NPT threads are here fitted into 1/2″ BSP hydraulic fittings.

Here’s the hydraulic oil sender installed in the drain line from the main propulsion pump, this should give me a pretty good idea of the temperature of the components in the system, the sender is earthed through the steel hydraulic oil tank.

The oil temperature sender is installed in the return line to the engine from the heat exchanger. This is measuring the oil temperature the bearings in the engine are being fed with.

The stack of heat exchangers is located on the starboard side of the engine bay, the large one here is cooling the hydraulic oil, the auxiliary pump is continually circulating the oil from the tank through this, then into the return filter on the top of the tank.

The engine oil is fed through this much smaller heat exchanger mounted on the back of the large hydraulic cooler, the last in the circuit before the water is discharged back overboard through a skin fitting.

As we’ve got the diverter block on the side of the engine where the oil filter should be, a remote oil filter is fitted above the fuel tank. The thermostat strapped on operates the main engine bay ventilation fans, switching them on once the engine oil reaches 60°C.

Posted on March 9, 2017April 24, 2017 by The Engineer — 5 Comments

Jaguar S-Type Aux Heater / Webasto Thermo Top V Part 1 – Teardown & Cleaning

Here’s another Diesel-fired heater related project – these Webasto heaters are fitted to Jaguar S-Type cars as auxiliary heaters, since (according to the Jag manual), the modern fuel-efficient diesels produce so little waste heat that extra help is required to run the car’s climate control system. (Although this seems to nullify any fuel efficiency boost, as the fuel saved by not producing so much waste heat in the engine itself is burned in an aux heater to provide heat anyway). The unfortunate part is these units don’t respond to applying +12v to Pin 1 of the ECU to get them to start – they are programmed to respond to CAN Bus & K-Line Bus only, so they require a bit more effort to get going. They also don’t have a built-in water circulation pump unlike the Webasto Thermo Top C heaters – they expect the water flow to be taken care of by the engine’s coolant pump.

The water ports are on the side of this heater instead of the end, the heat exhanger is on the left. These hearers are fitted to the car under the left front wing, behind a splash guard. Pretty easy to get to but they get exposed to all the road dirt, water & salt so corrosion is a little problem. The fuel dosing pump is in a much more difficult spot to get at – it’s under the car next to the fuel tank on the right hand side. Access to the underside with stands is required to get at this.

The ECU side has all the other connections – Combustion air, exhaust, fuel, power & control.

Only two of the external connectors are used on these heaters, the large two pin one is for main power – heavy cable required here as the current draw can climb to ~30A on startup while the glow plug fires. The 8-pin connector on the left is the control connector, where the CAN / K-Line / W-Bus buses live. The fuel dosing pump is also supplied from a pin on this connector. The small 3-pin under that is a blank for a circulation pump where fitted. Pinouts are here:

Pin	Signal
1	Battery Positive
2	Battery Negative

Pin Number	Signal	Notes
1	Telestart / Heater Enable	Would usually start the heater with a simple +12v ON signal, but is disabled in these heaters.
2	W-Bus / K-Line	Diagnostic Serial Bus Or Webasto Type 1533 Programmer / Clock
3	External Temp Sensor
4	CAN-	CAN Bus Low
5	Fuel Dosing Pump	Fuel Pump output. Connect pump to this pin & ground. Polarity unimportant.
6	Solenoid Valve	Fuel cutoff solenoid optionally fitted here.
7	CAN+	CAN Bus High
8	Cabin Heater Fan Control	This output switches on when heater reaches +50°C to control car heater blower

Pin	Signal	Notes
1	?	?
2	Circulation Pump +
3	Circulation Pump -

Removing the clipped-on plastic cover reveals the other ECU connectors. The large white one feeds the glow plug, & the large multi-pin below brings in the temp & overheat sensor signals.

The heart of the ECU is a massive microcontroller, a Freescale MC9S12DT128B, attached to a daughterboard hooked into the ECU power board.

The high power section is on the board just under the connectors, here all the large semiconductors live for switching the fan motor, glow plug, external loads, etc.

The bus transceivers are separate ICs on the control board, a TJA1041 takes care of the CAN bus. There’s also a TJA1020 LIN bus transceiver here, which is confusing since none of the Webasto documentation mentions LIN bus control.

The combustion fan motor is in the ECU compartment, nicely sealed away from the elements. There is no speed sensor on these blowers, unlike the Eberspacher ones.

The motor is a Buhler, rated at 10.5v.

Unclipping the cover from the other end reveals the combustion fan, it’s under the black cover. (These are side-channel blowers, to provide the relatively high static pressure required to run the burner).

The overheat & temperature sensors are on the end of the heat exchanger, retained by a stainless clip.

With the clip removed, the sensors can be seen better. There’s some pretty bad corrosion of the aluminium alloy on the end sensor, it’s seized in place.

The heater splits in half to reveal the evaporative burner itself. I’ve already cleaned the black crud off with a wire brush here, doesn’t look like this heater has seen much use as it’s pretty clean inside.

Inside the burner the fuel evaporates & is ignited. There is a brass mesh behind the backplate of the burner to assist with vaporisation.

The glow plug is fitted into the side of the burner ceramic here. This is probably a Silicon Carbide device. It also acts as a flame sensor when the heater has fired up. The fuel inlet line is to the left under the clamp.

The hot gases from the burner flow into the heat exchanger here, with many fins to increase the surface area. There’s only a couple of mm coating of carbon here, after 10 years on the car I would have expected it to be much more clogged.

I’m currently waiting on some components to build an interface so I can get the Webasto Thermo Test software to talk to the heater. Once this is done I can see if there are any faults logged that need sorting before I can get this heater running, but from the current state it seems to be pretty good visually. More to come once parts arrive!

The full service manual for these heaters can be grabbed from here, along with the wiring details for the Jaguar implementation & the Thermo Test software for talking to them:

[download id=”5618″]

[download id=”5620″]

[download id=”5622″]

Posted on December 6, 2016 by The Engineer — 13 Comments

Honda GX35 Clone – Are They Any Good?

In a word, no they aren’t any good. As usual, cheap doesn’t equal good, and in this case the cheapo clones are a total waste of money. Read on for the details!

I’ve been looking into using a cheap Chinese clone Honda GX35 engine to drive an automotive alternator as a portable battery charging & power unit. These engines are available very cheaply on eBay, aimed at the mini-bike/go-kart market.
For those not in the know, the Honda GX25/35 4-strokes are strimmer-type engines that traditionally were always of 2-stroke construction. Honda worked out how to have a wet-sump engine without the need to keep the engine always in the “upright” position. They do not require mixing of oil into the fuel for lubrication as 2-strokes do, so should be much cleaner running.

So far I’ve had two of these cheap engines, as the first one died after only 4 hours run time, having entirely lost compression. At the time the engine was idling, no load, having been started from cold only a few minutes before. Having checked the valve clearances to make sure a valve wasn’t being held partially open, I deduced that the cause was broken piston rings. This engine was replaced by the seller, so I didn’t get a chance to pull it to bits to find out, but I decided to do a full teardown on the replacement to see where the cloners have cut corners.

I’ve already stripped off the ancillary components: exhaust, carburettor, fuel tank, cowlings, as these parts are standard to any strimmer engine. The large black hose here is the oil return feed back to the rocker cover from the crankcase. The oiling system in these engines is rather clever. The main engine block is made of light alloy, probably some permutation of Aluminium. There is much flashing left behind between the cylinder fins from the die-casting process, and not a single engine manufacturer’s logo anywhere. (From what I’ve read, the genuine Honda ones have their logo on the side of the crankcase).

Here’s the top of the engine with valves, rockers & camshaft. All the valve gear up here, minus the valves themselves & springs, are manufactured from sintered steel, there are no proper “bearings”, the steel shafts just run in the aluminium castings. The cam gear is of plastic, with the sintered steel cam pressed into place. The cam also has the bearing surface for the pin that the whole assembly rotates on. The timing belt runs in the oil & is supposed to last the life of the engine, and while I’d believe that in the original Honda, I certainly wouldn’t in this engine. The black grommet is the opening of the oil return gallery.

Here’s the cam on the back of the plastic pulley. A single cam is used for both intake & exhaust valves for space & simplicity.

Just visible under the intake valve spring is a simple stem seal, to hopefully prevent oil being sucked down the valve guide into the cylinder by intake vacuum. Running these cheap engines proves this seal to be ineffective, as they blow about as much blue oil smoke as a 2-stroke when they’re started cold. 😉

The starter side is where the oil sump is located on these engines, along with the dipstick.

The flywheel end of the engine is the usual fare for small engines. Ignition is provided by a magneto, with a magnet in the flywheel. This is no different from the 2-stroke versions. As these ignitions fire on every revolution of the crankshaft, the spark plug fires both on compression, igniting the fuel for normal operation, and again into the exhaust stroke, where the spark is wasted.
One thing I have noticed about these engines is an almost total lack of cooling air coming through the cowling over the cylinder cooling fins. Plenty was flowing over the exhaust silencer side, I believe bad housing design would be what causes this problem. A lack of cooling certainly wouldn’t help engine longevity!

Separating the bottom of the engine was a little difficult, as there is a significant bead of sealant used instead of a gasket. Inside the sump of the engine are a pair of paddles, which stir up the oil into a mist. As the piston moves in the cylinder, it acts as a pump, creating alternating pulses of pressure & vacuum in the crankcase. Oil mist flows through a drilling in the crank from the sump, into the crankcase where it (hopefully) lubricates the bearings & the cylinder wall. Incidentally, the only main bearings are on the crankcase – the far end of the shaft that carries the oil paddles & timing belt is just flapping in the breeze, the only support being the oil seal in the outer housing. The crank itself isn’t hardened – a file easily removes metal from all parts that I could get at. The big end journal pin might be, but these cranks are pressed together so I can’t access that part.

The oil mist feeds into the crankcase through this hollow section of shaft, there’s a drilling next to the timing belt pulley to connect the two spaces together.

The lower crankcase is just a simple die casting, there’s a check valve at the bottom under the crankshaft to transfer oil to the rocker cover, through the rubber tube on the outside of the engine. After the oil reaches the rocker box, it condenses & returns to the sump via the timing belt cavity.

Removing the crankshaft from the engine block gives me a look at the piston. The factory couldn’t even be arsed to machine the crown, it’s still got the rough finish from the hot-forging press. This bad finish will pick up much carbon from combustion, and would probably cause detonation once enough had accumulated to become incandescent in the heat of combustion. Only the centre is machined, just enough for them to stamp a number on.

A look up the cylinder bore shows the valves in the cylinder head. These engines, like their 2-stroke cousins have a single casting instead of a separate block & head, so getting at the valves is a little more of a pain. The cylinder bore itself is a cast-in iron liner and it’s totally smooth – like a mirror finish. There’s not a single sign of a crosshatch pattern from honing. If the first engine that died on me was the same – I’d be surprised if it wasn’t, this could easily cause ring breakage. The usual crosshatch pattern the cylinder hone produces holds oil, to better help lubricate the piston & rings. Without sufficient lubrication, the rings will overheat & expand far enough to close the end gap. Once this happens they will break.

Finally, here’s the valves with their springs removed from the cylinder. These are the smallest poppet valves I’ve ever seen, a British penny is provided for scale.

In all, these engines share many components with the older 2-stroke versions. The basic crankshaft & connecting rod setup is the same as I’ve seen in many old 2-strokes previous, the addition of the rather ingenious oiling system by Honda is what makes these tiny 4-strokes possible. I definitely won’t be trusting these very cheap copies in any of my projects, reliability is questionable at the least. The apparent lack of cooling air flow over the cylinder from the flywheel fan is concerning, along with the corner-cutting on the cylinder finishing process & piston crown, presumably to reduce factory costs.

Posted on January 17, 2016March 12, 2017 by The Engineer — 6 Comments

Eberspacher Tent Heating System

The "Tenterspacher" — The “Tenterspacher”

I go camping on a regular basis here in the UK, and often even in summer it’s horribly cold at night in a field somewhere in the middle of Leicestershire. This doesn’t go too well with my severe aversion to being cold.
For the past several years I’ve used a Tilley lamp for some heat & light while at festivals & general camping, but it’s heat output is less than stellar when used in a 6-man tent.

An Eberspacher diesel heater was what was required for the job. Above is the unit as it’s built at the moment – I’ve used an old D1LCC 1.8kW heater that was recently decommissioned from nb Tanya Louise, as it’s getting a bit funny about what kind of fuel it’ll run on in it’s old age. It’ll work perfectly well on kerosene though – a fuel I already take with me camping for the Tilley.

It’s mounted on a base box, which is a repurposed steel electrical junction box that saw a previous life containing a 3-phase fan motor controller.

Here’s the info on the heater unit itself. Drawing 22W of power at 12v I’ll be getting 1.8kW of heat output – sounds good to me.

Here’s a view into the base box before the circulation fans were fitted, in early prototype stage. I used a small toroid as a clunk on the end of the rubber fuel line 😉

After a few bits from the Great eBay arrived, here’s the internals of the base unit at present. The fuel tank is a repurposed 2L fridge water container – made of tough HDPE so it’s fuel resistant.
The fuel pump is mounted on the left side next to the tank – having been wrapped in some foam to deaden the continual ticking noise it creates. The exhaust & it’s silencer are mounted at the rear, the silencer being retained by a surplus rubber shock mount. Luckily the exhaust systems on these heaters don’t get particularly hot, so the rubber doesn’t melt.
The exhaust outlet is routed through the frame, to be attached to an external hose. I don’t want combustion gases in the tent with me!

Standard Eberspacher silencers also aren’t gas-tight from the factory – they’re designed to be used in the open on the underframe of a vehicle, so I’ve covered all the seams in aluminium tape to make the system airtight.

To make sure that the support components don’t get overheated with the exhaust being in such close proximity, and to pull a little more heat out of the system, a pair of slow-running 80mm fans has been fitted to the end of the box. These blow enough air through to give a nice warm breeze from the vents on the other end of the base.

The tank I’ve used just so happened to be the perfect size to fit into the base box, and to tap the fuel off a bulkhead fitting was put into the top of the tank, with a dip tube on the other side. The fuel line itself is tiny – only 4mm.
If the specifications from Eberspacher are to be believed, 2L of fuel on board will allow the system to run for about 8 hours on full power, or 16 hours on minimum power.

Being inside the base, refuelling is a little awkward at the moment, the heater has to completely cool before the exhaust can be detached without receiving a burn, so I’ll be building in a fuel transfer system from an external jerry can later to automate the process – this will also help to avoid messy fuel spills.

More to come when the rest of the system is worked out!

73s for now!

Posted on October 7, 2014October 7, 2014 by The Engineer — Leave a comment

HPI Savage Petrol Conversion – Fuel & Silicone – Chemical Compatibility

While I was already well aware of the effects of petrol on silicone products – the stuff swells up & dissolves over a very short period of time, which makes it an unsuitable material for seals in a petrol fuel system.

I wasn’t aware the O-Ring on the fuel tank cap of the Savage is silicone, as can be seen in the image above it has swelled up to much larger than it’s original size. It’s supposed to sit in the groove on the cap & fit into the filler neck when closed.
This was only from a couple of hours of petrol exposure, now the seal is such an ill fit that the cap will not close properly.

The solution here is to replace the ring with a Viton O-Ring, 2.5mm cross section, 23mm ID. I assume the fuel tank is made of polypropylene – this should stand up fine to the new fuel.

Another concern was the O-Rings on the carburettor needles, however these seem to be made of a petrol-resistant material already & are showing no signs of deterioration after 24+ hours of fuel immersion.
The O-Rings that seal the engine backplate to the crankcase also seem to be working fine with the new fuel.

Another silicone part on the engine is the exhaust coupling, between the back of the cylinder & the silencer, I’m not aware of a suitable replacement as yet, although as it will mainly be exposed to the combustion products & not raw fuel, it may just survive the task.

The extra heat from burning petrol in one of these engines may also put a lot of stress on this component, if it eventually fails I may attempt a replacement with automotive hose – time will tell on this one.

I’m also not sure of the plastic that standard fuel bottles are made from – their resin identification number is 7, so it could be any special plastic, but I’m guessing it’s Nylon.
However according to the spec sheet for Nylon, it’s chemically compatible with petrol – yet the plastic appears to be getting softer with exposure, so it may be a special blend designed specifically for glow fuel.

Besides these small glitches, the engine is running well on it’s newly assigned diet of petrol, I’m currently running an 18:1 mix of petrol to oil (250ml oil to 4.5L of petrol), this seems to be providing more than adequate lubrication. While it smokes like a chimney, plenty of unburned oil is making it out of the exhaust, so the engine’s internals should have a liberal coating.
I’m yet to actually run the model out in open space so I can start tuning the mixture, but bench tests are promising.

More to come!

Posted on October 6, 2014October 6, 2014 by The Engineer — Leave a comment

HPI Savage X 4.6 Ignition Conversion – Initial Carburettor Settings & Module Mountings

The engine now with it’s required ignition sensor, it is now mounted back on the chassis of the model. I have replaced the stock side exhaust with a rear silencer, so I could fit the ignition module in place next to the engine.
For the mounting, I fabricated a pair of brackets from 0.5mm aluminium, bent around the module & secured with the screws that attach the engine bed plate to the TVPs. The ignition HT lead can be routed up in front of the rear shock tower to clear all moving suspension parts, with the LT wiring tucked into the frame under the engine.
In this location the module is within the profile of the model chassis so it shouldn’t get hit by anything in service.

New exhaust silencer fitted to the back of the model. This saves much space on the side of the model & allows the oily exhaust to be discharged away from the back wheel – no more mess to wipe up.

The ignition switch fitted into the receiver box. This is wired into channel 3 of the TF-40 radio, allowing me to remotely kill the engine in case of emergency. I have fitted a 25v 1000µF capacitor to smooth out any power fluctuations from the ignition module.
The radio is running from a 11.1v 1Ah 3S LiPo pack connected to a voltage regulator to give a constant 6.5v for the electronics. I found this is much more reliable than the standard 5-cell Ni-MH hump packs.

The stock silicone fuel tubing has been replaced with Tygon tubing to withstand the conversion to petrol.

High speed needle tweaked to provide a basic running setting on petrol. This is set to ~1.5mm below flush with the needle housing.

Low speed needle tweaked to provide a basic running setting on petrol. This is set to ~1.73mm from flush with the needle housing.

As petrol is a much higher energy density fuel, it requires much more air than the methanol glow fuel – ergo much leaner settings.
The settings listed should allow an engine to run – if nowhere near perfectly as they are still rather rich. It’s a good starting point for eventual tuning.