How would I measure RPMs in a diesel engine?

[jeroen74]

It's a simple one cilinder diesel... not automotive at all. No fancy ECUs and databusses.


Looks like this



I guess?

[Lifeboat_Jim]

Yes, scroll up to my detailed post. I also linked to the actual Lister Petter AD1 engine.

[NDT]

I still think that you should go with the hall effect sensor. And since you plan on monitoring other engine parameters, you also should go with the corresponding automotive sensors according with what you want to measure. The sensors that you need (hall effect for the crankshaft and propeller, temp sensor in the form of an NTC or PTC sensor for air, fuel, or other fluid, etc) are already available and specifically designed for engines, so, why reinvent the wheel? They are rugged, dependable, accurate, and cheap to not too expensive.

Could you expand on that please? NTC/PTC etc. I'm a complete n00b on electronics. Although Greg is quite handy on general electronics I don't think he'd know what those are either.

Of course... actually, it's very simple. NTC and PTC refer to Negative Temperature Coefficient and Positive Temperature Coefficient. These sensors are just resistive elements whose value changes with temperature. In a NTC, the resistance of the sensor decreases as the temperature increases; in a PTC you have the opposite case, as the temperature increases the resistance of the sensor increases also. In the automotive word these type of sensors, regardless of the temperature coefficient, come in two basic "flavours": CLT, which means coolant temperature sensor, for measuring the liquid coolant temperature, and MAT, or manifold air temperature, for measuring the temperature of the air entering the engine. The difference lays on the type of exposure protection of the sending element. There are also fuel temperature sensors, they are similar to CLTs, but I've never used them so I can't express an informed opinion. I think you should make a list of all the parameters that you want to measure and from then see which sensor you'll be using for what.
One other thing I forgot to mention: if you want to control the starting of the engine with the microprocessor, it's essential that you use a sensor system that gives you a lot of pulses per revolution, in order to stop the current flow to the starter in the right moment.

[arvidj]

When I was looking for a tachometer for three cylinder Yanmar Diesel in my tractor I found these:

This group decided that a sensor on the injector fuel line was a reasonable way to solve the problem: http://tinytach.com/new_features_diesel.php

Autometer like the "alternator" approach: http://www.autometer.com/productPDF/608.pdf, as did this group ... http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=128/prd128.htm

This fellow thought an optical sensor was a good idea ... http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml

I also looked at one of the many devices that would sense the teeth on the ring gear.

In the end I decided that most of the implements I use on the tractor require that I run it WFO so a tach would not be of great value. But the research did show that "the problem already has several reasonable solutions", one of which might be applicable to your situation.   

[G7PSK]

Its a Petter then. I have rebuilt many of those in my life. The injector pump is a CAV bosch type two things come to mind one the injector pipe has a distinctive pulse so a strain gauge on that might work or a piezo. the other is inside the pump under a small cover is an adjustment screw this goes up and down with the plunger it would be possible to arrange for a contact to touch this at  some point.

[G7PSK]

I dont have the service book for the AD1 but do have it for the AA1-AB1 this is the smaller brother of the AC1-AD1 they also made an AC2-AD2 twin cylinder which was very popular for mobile welders at one time.
Any way I have had a look at the book and a number of thoughts arise the best option is probably to use a sensor (hall) on one of the extension shafts, I don't know how the drive is taken on your engine but there was three options flywheel either direct or with a shaft extension a crankshaft extension  on the other end an a half speed shaft as an extension of the camshaft this shaft is transposable from crank to cam just swap the covers over or you can have two shafts.
There is another way you could use a valve rocker. There is also a number of holes drilled into the flywheel for balancing purposes which might also be used with a hall sensor.
What you don't want to do is disturb the pump timing as they are a pig to time, it has to be don by finding the spill postion and adjustment is made by adding or removing shims under the pump, I have had to do this in the past and to get it dead right can take half a day, most people don't go this far but done right these engines will run like sewing machine.

[fcb]

Why make life difficult?  If you have a ring-gear, then just fit an standard crank angle sensor from a car, they're a tenner (new) from ebay etc.. and someone else has made them oil/dust/waterproof and neatly connectorised it for you...

[Anks]

Thinking outside the box you could always use the waveform generated by the alternator if it has one. Just tap it before one of the diodes. Also depending on how the charging system is designed you could a current meter to see this.

[Lifeboat_Jim]

Ladies & Gents, Boys & Girls...

Many thanks for all the suggestions.

Alas the Lister Petter AD1 engine is being very naughty and not playing ball (low compression), and I've run out of time and talent. My mechanical knowledge is as poor as my electronics obviously, and now it's down to stripping down and regrinding valves/pistons etc.

I bought it with an Air Compressor head attached to drive a Shot Blaster so it was a means to an end. I then thought to take off the Compressor and put a GenSet on and continue to use it (possibly switching the Compressor head back in for occasional future use).

I will persevere with it but with winter coming and time against us its time to just hire in a Compressor and crack on with the main project so this aspect will have to be parked for a few months :-(

Having said that, the thought process of 'measuring RPMs' in a simple diesel engine was valuable and directly transferable to the main marine engine. Plus I have hopes in the future for the little AD1 (if not this one, another) with more time, effort and a little cash.

For the AD1 it looks like the teeth of the Gear Ring is the way forward (or the flywheel, which has one cut out on its outer edge), not all AD1 have Gear Rings but at least this one does.

Many thanks for all the help/assistance. Special shout out to G7PSK who has gone the extra mile with much advice via e-mail/PM.

No doubt Greg and myself will be back to pick your collective brains with regard to other aspects of this project in due course. I know there has been some flaming of attitudes in this 'Beginners' Forum but you've been fantastic to Greg & myself... which is nice ;-)

o7

@ Anks... no alternator
@FCB... Agreed. Didn't know what they were called nor the pro's/con's compared to other methods.

[Anks]

Ladies & Gents, Boys & Girls...

Many thanks for all the suggestions.

Alas the Lister Petter AD1 engine is being very naughty and not playing ball (low compression), and I've run out of time and talent. My mechanical knowledge is as poor as my electronics obviously, and now it's down to stripping down and regrinding valves/pistons etc.

I bought it with an Air Compressor head attached to drive a Shot Blaster so it was a means to an end. I then thought to take off the Compressor and put a GenSet on and continue to use it (possibly switching the Compressor head back in for occasional future use).

I will persevere with it but with winter coming and time against us its time to just hire in a Compressor and crack on with the main project so this aspect will have to be parked for a few months :-(

Having said that, the thought process of 'measuring RPMs' in a simple diesel engine was valuable and directly transferable to the main marine engine. Plus I have hopes in the future for the little AD1 (if not this one, another) with more time, effort and a little cash.

For the AD1 it looks like the teeth of the Gear Ring is the way forward (or the flywheel, which has one cut out on its outer edge), not all AD1 have Gear Rings but at least this one does.

Many thanks for all the help/assistance. Special shout out to G7PSK who has gone the extra mile with much advice via e-mail/PM.

No doubt Greg and myself will be back to pick your collective brains with regard to other aspects of this project in due course. I know there has been some flaming of attitudes in this 'Beginners' Forum but you've been fantastic to Greg & myself... which is nice ;-)

o7

@ Anks... no alternator
@FCB... Agreed. Didn't know what they were called nor the pro's/con's compared to other methods.

Just noticed what sort of engine it is sorry. I would go with an hall sensor on the crank simple and effective.

[Lifeboat_Jim]

Yep.

Hall Effect was always my favourite option. However we'd never thought of a Crank Angle Sensor (aka Crank Position). The flywheel does have teeth of course.

Much time has passed in getting the bloody engine working and in tip top condition. That's done now.

Yesterday the Postie brought one of those cheap Laser Tachos, and I'm looking at what ebay has to offer for a Crank Sensor... need a small diameter to fit, ideally 12.5mm/ half inch. Motorcycle sensor perhaps.

[trackman44]

I would use the crank timing wheel from a Ford Escort engine and it's sensor, very reliable and no worries about dirt contaminating an opto sensor arrangement. If you can get to a scrap yard and get the timing wheel and sensor (the timing wheel has 35 teeth plus one missing tooth) you could measure for the missing tooth ( it is an ac signal with a train of 35 cycles and one missing).This arrangement is used in an electronic ignition system called MegaSpark (It's part of the MegaSquirt DIY fuel injection system), here's a link :-

http://home.comcast.net/~tjhafner/SparkManual.html

Good luck with the project.

Will