On: Autophage rocket engine consumes plastic fuselage ...

[skykooler]

What are the exhaust products of HDPE? Any larger molecules will reduce the exhaust velocity, which will lower the specific impulse compared to methane even if they are producing the same amount of energy.

[marcosdumay → skykooler]

With the correct mixing, water and CO2.

The real question is what is the rate of heavy molecules, or equivalently "how correct is the mixing"?

I imagine those first prototypes weren't that good.

[userbinator → skykooler]

Perfect combustion yields H2O and CO2, same as methane.