Soot Formation in a Multipoint-Fuel-Injected Spark-Ignited Engine

Higher levels of carbon in the oil of some multipoint-fuel-injected spark-ignited engines have been observed relative to carbureted and/or Throttle-Body-Injected (TBI) systems. These higher carbon levels could potentially shorten the oil change interval or cause engine wear. It has been theorized that carbon in the oil is caused by soot produced during the combustion process. Vehicle tests were run to show that this soot has no environmental impact. This paper discusses soot formation and how to minimize this formation by controlling injection parameters (direction, timing, method, and spray) and engine conditions (speed, load, coolant temperature, EGR rate, inlet air temperature, and spark advance). Effects on engine emissions and peak cylinder pressures are also addressed.