[Mgs] Engine maths...and spare time

[Richard Lindsay]

Hey friends,
   Over on the Triumph TR3a group, my friend Randall posted a picture of a
TR3 piston, damaged by 'knock'. I thought I would share it here. See
attached.

R

On Sun, Apr 5, 2020, 6:54 AM Richard Lindsay <richardolindsay at gmail.com>
wrote:

>    Max, as Paul says, finding the sweet spot is the key and it's a moving
> target! Take a look at the attached scan from Campbell's book on sports car
> engines. Notice please the pressure curve and how it doesn't really rise
> much at all until well after the spark alights the charge on fire - perhaps
> only doubling cylinder pressure by TDC. So although lighting off the charge
> before TDC would appear to reduce power, the negative effect is minimal
> when compared to placing the six-fold pressure increase where it can do the
> most work.
>    Paul, *et al. *have astutely pointed out the counter-productive and
> even damaging effects of pre-ignition and 'pinking', or 'pinging' as we say
> here in the States. Both of these phenomena are potentially damaging to the
> engine. And their occurence is a whole other topic - if somewhat allied to
> timing. Here's just a teaser and stated at the limits of my knowledge.
>    Pre-ignition is as the word describes, when the charge is ignited
> before ignition by the spark. That can happen in high compression petrol
> engines by dieseling. That is, ignition by the heat of compressing the
> charge alone, or by some 'hot spot' within the combustion space. E.g. the
> plug's tip or a glowing carbon buildup. Pinking is believed to be caused by
> the 'end gas' flash-burning all at once rather than progressing smoothly.
> It's rumored to have gained its name from the sound it makes. Again, I am
> paraphrasing words from Campbell, not claiming intimate knowledge.
>    Suffice to say, so many poorly understood things are happening in a
> running engine, it's no wonder that most parameters are set, or at least
> fine tuned, by testing rather than modeling. Repeating: "Practice always
> works in theory, but theory doesn't always work in practice."
>
>    Thank you everyone for your questions and answers. Fascinating topic.
>
> Rick
>
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