123 / | HD | INTERNAL-COMBUSTION ENGINES |
434 | DF | CHARGE FORMING DEVICE (E.G., POLLUTION CONTROL) {29} |
536 | .~ Combustible mixture ionization, ozonation, or electrolysis {3} | |
537 | DF | .~.~> Before intake valve (e.g., in manifold) |
538 | DF | .~.~> Fuel only |
539 | DF | .~.~> Air only |