First,this is what I understood from theory: If I understood the concept of 'engine stall' correctly,it occurs as a result of the engine not having enough time to adjust for a increased load. As a practical example of engine stall,I consider the instance of 'letting go of the clutch pedal' too quickly. When I shift into first gear and let go of the clutch pedal all of a sudden,the engine stalls. I am guessing this is because the engine is 'suddenly' subject to a heavier load and its rpm dropped so low that it couldn't supply enough air to combust the fuel. This brings me to the question of the hydrogen Otto engine cars. One of the main properties of hyderogen(this paper says so http://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm03r0.pdf) is its 'HIGH RANGE OF FLAMMABILITY'. This means that a hydrogen Otto engine car could run at lower rpms than a gasoline engine.So,I infer that hydrogen Otto engine cars didn't stall(back in the 60's) when you let-go of the clutch all of a sudden. Is my inference valid? Does anyone here have experience with hydrogen-powered cars?