Hello and welcome to this video on running compression
The purpose of this video is to assist you in being able to identify
All the events that take place in a running compression waveforms
Before we take a look at a live waveform and how to analyse that waveform
We are going to take a quick look at how to set up the hardware
That is required to carry out this test
Therefore if you take a look at the video in the bottom right hand corner of the screen
You can see that I am using the WPS500 pressure transducer
And that this has been connected to cylinder 1 of the engine
In terms of setting up the transducer all we need to do is turn the transducer on
Allow it to go through the self calibration process
And once this has completed we just need to ensure that it is set to range 1
This is because we could be looking at pressures anywhere
From 20 all the way to 34.5 Bar
In terms of running the test we do need to ensure that no fuel
Can enter the cylinder in which we are testing
In most cases this can simply be done by disconnecting the fuel injector
We also need to ensure that we can isolate the ignition supply from that cylinder
And if we are working on a vehicle with a COP ignition system this can easily be done
By disconnecting the COP unit and removing it from the engine
If however you are working on a distributor or a DISS type of ignition system
Then we need to take our HT cable and connect this to a stable ground point
On the engine as this will ensure that no damage will occur
To any of our ignition components
What I am going to do is start the engine up so we can
Look at a live running compression waveform
If you take a look at the waveform on the screen
You can see that I have an injector signal
And I also have a secondary ignition signal
The reason I have done this is that it can help us to
Identify all the events that are taking place
And the timing of those events
To get a better idea of what is going on I am going to load a waveform
That I took earlier in which I have added some events and detail
I shall go ahead and load it up
You can see by looking at this waveform that I have identified the piston position
By putting TDC and BDC across the top of the screen
You can also see that I have identified the four stages of the cycle
Power - exhaust - intake and compression
You can also see that I have tried to identify the valve opening times
So we have our exhaust valve opening and closing
And our inlet valve opening and closing
So if we start to analyses the signal we can see if we start on the left hand side
At top dead centre on our power stroke
We know that our piston is going to travel all the way to
Bottom dead centre in this process
And we can see that during this process our pressure has reduced
And this is as a result of the piston movement
We can also see that our pressure returns to a negative pressure
And this is because no combustion has actually taken place
And we are looking at the cylinder as essentially an air pump
Therefore the pressure we started with should be the pressure that we end up with
Now if when you come to carry out the test you end up with a lower amount of depression
I.e a slightly higher pressure this could be one of our valves
I.e the inlet or the exhaust valve or even the piston rings are not sealing properly
And we have leaked out some of our air
We can also see that towards the end of this cycle the exhaust valve has begun to open
We can see this by our pressure starting to increase up to zero
If we take a look at the exhaust stage now we know that our piston is
At bottom dead centre and it is going to travel all the way up to top dead centre
We know that our exhaust valve is fully open
And what we can see here on our compression signal
Is that we have these ripples taking effective
Now these are caused as the piston travels up the cylinder
And it is pushing all the air out through the exhaust valve
We can also see that towards the end of the exhaust valve that our inlet valve
Has begun to open and we have this period of valve overlap
This then takes us into the inlet stage of the cycle
We know that our piston is now at top dead centre
And is going to travel all the way down to bottom dead centre
We see that we have these ripples created again
This is as air is being induced into the cylinder past the intake valve
We can also see that our exhaust valve is now fully closed
And our intake valve is still open and we are inducing air into that cylinder
This then takes us into the compression phase
In which the piston is now at bottom dead centre
And it is going to travel all the way up to top dead centre
We can see that our intake valve is closing and that after this
Our pressure starts to build back up
This is because the piston is now compressing the air in the cylinder
As it rises back up to top dead centre
Then essentially the cycle repeats itself
And this is how to interpret a running compression waveform
Now what I am going to do is pull up the waveform again
The live one so we can take another look at that
You can see that my pressure is now 5.8 to 6 bar
You may be thinking that this does not tell us the
Correct pressure that the cylinder is able to produce
So I am going to show you now how we can get that information
So what I need to do is slightly tweak this waveforms
And I will talk you through what I am going to do
I am going to remove the injector signal as we do not need to see that any more
I am also going to remove the secondary signal as we do not need that either
I am going to change the setting for the transducer
As now we will be looking at much higher pressure
I am going for the full range up to 34 bar
I am also going to bring in channel D as I have connected this up to the mass airflow meter
I am going to set this to 10 Volts so it gives us our 5 Volt range on the top
I am now going to change my trigger so I am moving the trigger threshold up to 10 bar
So you can see now that we are not triggering on anything
I am going to change this to single capture
I am also going to change the timebase to a much longer timebase
So we are streaming I am going to go for 1 second across the screen
You can see now that we are streaming
I am going to bring the trigger over to 30%
So we can capture the whole event on the screen
I am going to make sure that I have filtering on my mass airflow metre
As we do know that this is a dirty signal like lambda and MAP
And our output could be slightly noisy
There we go I am just going to activate the filtering now
I am going to bring the video feed up so you can watch as I go wide open throttle
Then we will go wide open throttle
And this should tell us the maximum pressure that this cylinder is able to produce
You can see that the engine did not like that however we did achieve t
A pressure of just under 25 bar
So that tells us what the cylinder is able to produce
I hope that this video has been of some assistance and helps you to understand
The running compression waveform
And how to get a maximum pressure reading out of a cylinder
Thank you for your time