The combustion engine has been a vital part of lives since its invention in the late 19th century. Ever since then, refinement and analysis of how combustion occurs has taken up many hundreds of hours to get to the stage at which we find ourselves today. In this essay, I aim to compare combustion under ‘normal’ operating conditions to combustion under what is considered to be ‘abnormal’ operating conditions. In particular this essay will attempt to give an insight into the phenomenon of ‘knock’ in a homogeneous charge spark-ignited engine. A literature review followed by a discussion of what ‘knock’ is, factors affecting it, including its main causes and effects will make up the main body of this essay.
In order to discuss the topic of knock in engines properly, it is important to understand what are deemed to be ‘normal’ and ‘abnormal’ combustion. Normal combustion is defined in ‘Internal Combustion Engine Fundamentals’ as a process in which:
“The fuel and air are mixed together in the intake system, inducted through the intake valve…show more content… Taking this definition and comparing to other writings/articles, the paper from International Journal of Automotive Technology defines abnormal combustion by comparing it directly to normal combustion, in saying that the main difference “occurs when the flame does not propagate evenly and smoothly through the combustion chamber”. The information given in the journal is also important to consider when attempting to gain an understanding of the concept of abnormal combustion, it adds to what is considered the definition of abnormal combustion and also gives a futher insight into what is known to