In past decades humans used to travel on their own from one place to another place. This self-
dependent travel life was time-consuming and challenging. One of the greatest inventors, Rudolf
Diesel, invented the diesel engine in the 1890s; this significant technological
development became a part of the human lifestyle. The piston-cylinder arrangement converts fuel's
chemical energy into mechanical energy to power the engine, driving utilities such as trains, cars,
trucks, and marine vessels . Diesel engines usually operate with a higher compression ratio
vis-à-vis gasoline engines, leading to high thermal efficiency. Also, the diesel engine is
well known for transportation using light-duty and heavy-duty vehicles because of superior fuel economy, better drivability, and lower mass.
Hydrocarbons are produced due to the incomplete combustion of the air-fuel mixture.
Unburnedfuel molecules are recombined and form intermediate compounds known as HCs.
Also, sometimes lubricating oil particles stick on the cylinder walls and come out in the form
of HCs, generally minimum for engines. HC emissions discussed here are of gaseous states. HCs
forms in liquid/solid-state are categorized as particulate matter discussed separately in other
sections. HC forms from the fuel drip from injector sac volume and lean mixtures formed during
the ignition delay in heavy-duty engines. Also, flame quenching within crevices, oil release, and
storage are the sources of the HCs. These all are regarded assources of HCs for light-duty
engines and are considered asource of HCs . HC emissions are generally used to judge how
efficiently combustion is taking place during various operating conditions.HC emissions are
always believed to be a red emission pollutant as it is responsible for depleting ozone levels and
photochemical smog when it reacts with NOx.
Carbon monoxide (CO) is an odourless, colourless gas produced due to fuel's incomplete
combustion. Incombustible fuel can result inCO due to oxygen deficiency, lowtemperature, and
insufficient residence time for the combustion process . Also, it is known as highly toxic
gaseous emissions. CO forms during the process of HC formation, which can be understood by
the below-mentioned chemical reaction process
