Various data acquisition from Internal Combustion Engine (2 stroke)

[Vag 1-2]

Hi all!

I am a college student working on two stroke engines and I would like to create a system to monitor a few parameters for tuning and  purposes. I am a youngling in Labview and DAQ systems, but I like experimenting and learning along the way. I also try to avoid ready-to-use solutions, as much as possible.

I would like to acquire data for:

> RPM

> Temperatures; from various spots, such as intake, head, exhaust port, transfer port, crankcase etc

> Air-fuel ratio

> Knock/detonation

> (potentially) pressure traces over one cylce

Also, the plan is to export the data to a spreadsheet file in the future; something like a data logging function.

I have a MCC usb DAQ model 1208FS (http://www.mccdaq.com/usb-data-acquisition/USB-1208FS.aspx), so I have to use MCC's VI's.

I know I step into deep water with limited knowledge, but anyway.

I found a paper named "Development of a High-Speed DAQ System for Ignition Engines" by Cory Criswold, which gave me a rough idea on sampling rates and sensors.

I chose to start from what looked easier, ie temperatures: I purchased some K-type thermocouples and built the necessary amplifiers. I found many thermocouple VI examples and managed to built the VI needed. I haven't included any data logging function yet though.

Here it is:

Acq Temperature

Problem here is that MCC's vi's for Temperature Input, doesn't support cold junction terminals. Would there be any way to bypass that?

I would be gratefull if you took a look for any other mistakes!

Now, to come to the real problem: I have to measure the RPM, so that I can plot with AFR, temperature and detonation values. I found a few info on the web about systems using rotary encoders, but only in 4 cycle engines and with limited amount of rpm. A two cycle gasoline high-performance engine would go up to 15k rpm - especially those of small displacement I deal with.

Would I be able to use the same system the CDI uses to monitor RPM?

The Crank Position Sensor (CPS) is a 2-wire inductive pick-up and there is one lobe on the flywheel to trigger a signal. Like this:

http://users.uoa.gr/~sph0800108/modenas_dinamik_forum/DAQ/78mm_generator_.jpg

I assume I have to measure the frequency, but how will I convert that to RPM? 

Also, the CDI has an output signal for a tachometer. Could I use that or would it be more complex?

e.g. excuse for any wrong terms or expressions, I do my best but english is not my native language and I 'm not yet familiar with all the terminology in electronics and DAQ systems.

[Henrik_Volkers]

15k rpm is 250Hz, with 50kSps about 200 Samples per revolution, so your resolver shouldn't have more that 100 pulses per revolution ....

(I don't expect that the DAQ support incremental encoders by hardware decoding, so you might have to capture it and do the decoding in software)

If you capture the analog frequency the tone detection vi will give you the fundamental frequency f. f/n*60 give the rpm (n is the number of pulses per revolution)

You can build your own by using any gear wheel (with less than 100 teeth) a relay coil and a small magnet ( same physics than a guitar pickup 😉 )

You can build your cold junction by using a NTC as a temperature sensor and place it in good termal contact at your TC->Copper analog input connector

silicone a screw connector block on a aluminium bar together with the NTC and place it a small styrofoam box ....

But AD, TI, linear make nice TC amplifier with build in CJ compensation.. just ask for samples

Have fun

[Vag 1-2]

Starting backwards, I have found these amps from AD in the past, but there was not buy-per-unit option from the distributors in my country. http://www.analog.com/en/mems-sensors/digital-temperature-sensors/ad8495/products/product.html

I had given up on that facilitaion but thanks to you I looked them up once more and fell upon the AD595, which I have found in ebay.

It will be a lot more handy and easier to build.

Thanks!

As for the RPM now.

Firstly, thanks for the input on freq to RPM conversion via software. I think I can do it, it seems simple!

The sampling confuses me though.

My thinking is: rotor (flywheel) has a single lobe/teeth/protrusion, so when it passes below the proximity sensor, it creates one square-like pulse. At 15k rpm or 250rps, it would create 250 pulses. I would then need a sampling frequency of >500Hz (500 samples per sec) to get a proper signal. So, I wouldn't be even close to the sampling limit of the DAQ.

Is that incorrect? I don't know, most similar cases I found online indicate huge sampling rates, but they're all 4 strokes, where teeth count is far above 1.

[Henrik_Volkers]

If you have 250 /2 ignitions per second I bet you would like to have more information about what is happening between two ignitions 😉

With 50kSps you have 400 values between two ignitions, 200 values per revolution. So your resolution for the igniting point is about 1.8 deg (adding some stats it might get smaller.... )

Soundcards go up to 196kSample@24bit nowadays. Linearity is worse and no DC but hey, for higher order vibration analyses the cheapest way 😉