Boost pressure 1 Carbon 1 Carbon-free 1 Carbon-free fuel 1 Downsizing 1 Efficiency 1 Engines 1 Environmental impact 1 Equivalence ratios 1 Full-load 1 Gasoline 1 Gasoline engines 1 Hydrogen 1 Lean burn Mixtures 1 Performance 1 Spark-ignition engine 1 carbon-free fuels 1 downsizing 1 hydrogen 1 lean burn 1 spark-ignition engines 1