<div class="htmlview paragraph">An experimental study of a naturally aspirated, spark-ignited prechamber mounted in a CFR engine demonstrated that this system provides a marked improvement in lean-mixture combustion both before and after engine warm-up. In the system tested, a premixed fuel-air mixture containing five times the stoichiometric amount of fuel was supplied to the prechamber at a rate of 2% of the main chamber mixture flow. The fuel-rich flame issuing from the prechamber provided an ignition source capable of igniting main chamber mixtures much leaner than those normally ignitable by a standard spark plug.</div> <div class="htmlview paragraph">There are many advantages and disadvantages when comparing the standard CFR engine with the prechamber CFR engine. This paper goes on to explain the prechamber engine in detail and to compare it with the standard engine.</div>