Is it practically possible to run an IC engine with air rather than fuel by using a high pressure compressed air(400 bar)?
YES.
That is how compressed air is usually used.
You can get power tools that operate much like an Internal Combustion engine but they get their power from the compressed air instead of the expansion of burning fuel.
It is not free power, of course. It takes power to generate the compressed air.
There has even been a car made that used a tank of compressed air instead of fuel.
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