Should be relatively easy to build a spring piston that won't detonate.
A brass cylinder sleeve, close tolerance hyper-eutectic aluminum piston, and gapless steel compression ring seal.
No lubricant, hence no fuel to detonate.
If the ring were the right alloy stainless, water would make an OK lubricant. ( but would flash to steam )
Be interesting to repeat the experiment with such a rig.
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