Seldom does the EPA ever put out interesting research
but the research paper where they took a VW TDI diesel engine
retrofitted it with a sparkplug
and ran it on 100% Ethanol in the gasoline like Otto cycle
without lowering the factory TDI compression ratio
is well worth reading.
They ran EGR amounts from zero to over 50%

I wish they had made a few runs with Triptane,
the chemical invented by the USA council of fuel research prior to World War II
that Colonel Jimmy Dolittle knew about
and used to make 130 Octane aviation gasoline
for his famous bombing mission over Japan.