Starter Torque

[R_squared]

The third waveform is from a 1991 Honda Civic, 4 cylinder, 1493cc engine. The compression ratio is approximately 9:1. The inrush current equals 584 amps, but only for 20 or 30 milliseconds. The below ground potential spikes, to the right of the inrush peak are secondary ignition firings. The distributor cap was close to the battery cable and current clamp.

 

[nomad]

I roughly calculated the area under the curves in all these three graphs and found all areas are more or less same, meaning that total energy to start the engine is more or less same for all these three engines. Peak energy level can be higher at first (big 6 cyl.) engine, but it's application duration is shorter than the others. You have the data (coordinates of the curve) - so, you can calculate the areas under the curves at your computer easily. Maybe, my rough calculation was very rough and computer integration may give a very different result and those areas under the curves are very different. Also, I am wondering how you are comparing the starter motors of different engines with different sizes, stroke lengths and volumes. What's your dimensionless parameter that makes you think that waveforms of 6 cyl. diesel engine and same cyl. same volume gasoline engine would be much different and that the diesel would absorb more energy than the gasoline during the starting periods? I mean I am just wondering how you arrived at such a conclusion from these graphs that the diesel motor is spending more energy?

 

[Soundguy]

</font><font color="blue" class="small">( I roughly calculated the area under the curves in all these three graphs and found all areas are more or less same, meaning that total energy to start the engine is more or less same for all these three engines )</font>

</font><font color="blue" class="small">( I am just wondering how you arrived at such a conclusion from these graphs that the diesel motor is spending more energy? )</font>

First.. I -havn't- done any calculations based on the data. However.. you yourself in the first line stated that you had.. lets go with that for conversation sake.

What that means is: the small diesel and big gas both consumed the same power to start.

What can we infer from that: that CI per CI .. the diesel needs more power to start. As it took the same power to start a small CI diesel compaired to a larger CI gas. Thus a diesel the same ci as that big 6cyl gas should take more power to start than the 6cyl gas.. assuming equal ci...

Again.. I made no calc's.. just using what you have stated. Seems your first line provides the basis against the argument/question in your last line... In other words.. you answered your own question..

Soundguy

 

[nomad]

Well... I can say nothing. You are right
Congrads and thanks.

 

[johnk]

I always knew there were experts on this board. Now I know for sure. Thanks for all the inputs. I'll send this link to my son and he'll still say he is right. Take care and fine job.....

John

 

[R_squared]

I'm glad that Soundguy picked up on the subtlety - he is sharp. Here is another waveform from a 1998 Honda Accord, 6 cyl, 2997cc engine. The compression ratio is 9.4:1. I was not sure about posting it because the battery is the original and is at least 5 years old. The Accord engine still starts very quickly. The inrush current was 712 amps and it's duration was 50 or so milliseconds. We use synthetic oil in the Accord and tractor. The F150 and Civic gets the same dino oil.

 

[R_squared]

I don't use my Stewart Warner compression gauge very much anymore when testing cylinder compression. It's easier to perform a relative compression test with a lab scope and a quality current clamp. You disable the fuel pump or trip the inertia switch, trigger off the #1 cylinder and observe the starter current waveform. The starter current waveform displays each cylinders compression peaks and dips. Notches in the waveform usually indicate valve problems. A lower peak relative to the other peaks usually means worn rings in that cylinder. A relative compression test is not an absolute, but it's a good starting point.

 

[Soundguy]

</font><font color="blue" class="small">( I'm glad that Soundguy picked up on the subtlety. )</font>

Well.. I try.

If you ask my frioends.. they'll probably say I'm very trying! /forums/images/graemlins/shocked.gif

Soundguy

 

[nomad]

Now, a new question arised and that may make us re-think everythings in this thread.

Here are the engines I put under consideration:

1) 1998 Honda Accord, 6 cyl, 2997cc engine, compression ratio is 9.4:1.

2) 1991 Honda Civic, 4 cylinder, 1493cc engine, compression ratio is approximately 9:1.

Engine (1) is bigger than (2) as seen above. But their waveforms are showing that bigger engine (1) is spending less energy than the smaller (2) to start. So?

 

[uhmgawa]

</font><font color="blue" class="small">( Now, a new question arised and that may make us re-think everythings in this thread.)</font>

This not what I would call a rigorous experiment. There are other
sources of rotational resistance seen by the starter such as
alternator, water pump, cooling fan, and whatever mass is engaged
to the flywheel -- most of which present both inertial and
continuous loads. It is unlikely they are identical in the above three
cases. Additionally there is no way to guarantee the horizontal
width of each curve (starter engagement time) was the ideal of
being minimally sufficient to start each engine. The area under each
curve corresponds to the energy consumed by the starter without
differentiating between the percentage transformed to rotary
motion vs. heat (ie: starter efficiency) which are also unlikely to be
identical.

The other issue to keep in perspective is the inability to draw a
conclusion from effectively three data points taken at random.