The gasoline piston engine may have a future, but that future may not include spark plugs. Here’s one advanced approach known as Entry Ignition.

A critical fact about the gasoline piston engine that, among enthusiasts, isn’t widely understood: power and efficiency are essentially knock-limited. In a spark-ignition (SI) engine you can only squeeze air and fuel so tightly before it auto-ignites, converting useful combustion into damaging and inefficient knock. As a result, there’s an effective limit on compression ratio (and for boosted engines, intake pressure) and thus an ultimate ceiling on engine output and efficiency. You can’t get around Mother Nature.

One traditional way to turn auto-ignition to our benefit is the diesel aka compression ignition (CI) engine, but it has some well-known issues, including dirty emissions. Another approach is Homogeneous Combustion Compression Ignition, HCCI for short, but not all the bugs have been worked out there, either.

Yet another potential solution just now peeking into view is called Entry Ignition, where a pre-compressed air-fuel mix is pushed into a hot cylinder where it ignites on entry—hence the name. Entry Ignition is a departure from the familiar four-stroke cycle in a number of ways, with multiple compression and expansion phases and components not found in current production engines. (For a deep dive see the SAE paper by Peter C. Cheeseman.)  There’s a lot to absorb, but fortunately Jason Fenske of Engineering Explained has applied his clear and methodical approach to the matter, and somehow he managed to bring it home in just 13 minutes. And along the way, he included a concise explanation of the SI, CI, and HCCI processes as well. Bravo, Mr. Fenske. Video below.