The present paper tries to investigate the fundamental aspects of air pollutants, fuel properties, and engine performance during transient operation of naturally aspirated and turbocharged diesel engines in addition to comparing them to new experimental results using methanol as an oxygenate additive. The additives that can reduce the soot emission are various oxygenate alcohols (methanol, ethanol, and n-butanol). The additives that are used for improvement of the fuel properties (cetane number enhancers) are tertiary additives. Meanwhile, the additives used for increasing the engine performance are nanometallic additives, such as, silica, alumina, cerium, and manganese. This research demonstrates the effect of various additives on the performance of the diesel engine, emission, and diesel fuel properties by different models, to address the optimum and best conditions. This paper shows the effect of different oxygenate additives on the reduction of the soot formation, although this effect was different in the different models adopted. This research also illustrates the effects of tertiary additives and nanometallic additives on the fuel properties and engine performance, respectively, owing to the type of additive (additive name). Moreover, this paper examined the effect of other conditions (engine load, engine speed, and injection timing) on the above-mentioned responses.