compressionIgnition

Given a predicate that represents a relationship or action between entities, generate a one-sentence description explaining its meaning.  
# Instructions
Focus on describing the relationship, not the entities themselves. 
# Response Format
Begin the description with \' Indicates...\'

Predicate: compressionIgnition

Indicates that an engine or combustion process is initiated by compressing the fuel–air mixture until it self-ignites, rather than by an external spark.