Methods for evaluating the purity and combustion characteristics of motor fuels

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This article is the fourth in a series of articles aimed at introducing common methods for evaluating both conventional and alternative fuels. In previous articles, we focused on the determination of elements and non-hydrocarbon compounds, as well as the evaluation of physical and chemical properties. This article focuses on other not yet-discussed properties such as gum content, total impurities, ash content, carbonization residue, octane number, cetane number, and cetane index. The main goal of the article is to provide an overview of which fuels are used, why these properties are monitored, and what methods are used for this monitoring. Emphasis is placed mainly on standardized tests, but in some cases, additional tests not required by the standard are also discussed. Conventional and alternative fuels must meet the technical requirements defined by the relevant product standards. The fulfillment of these requirements is to ensure that, in addition to other properties, the relevant fuel will be of good quality and that the engine will not be damaged during its use. In addition to the technical requirements for fuels, the product standards also define the tests that are used to verify that the fuel meets the defined requirements. As mentioned above, this article is another in a series of articles aimed at presenting methods for evaluating both conventional and alternative fuels. In this article, we present an overview of the properties of fuels that have not yet been discussed in this series of articles. These are properties associated with the content of impurities present in the fuel (total impurities) or those impurities, or products that may arise during thermal stress on the fuel in the combustion system (ash content, carbonization residue, gum content). Furthermore, in this text, we will focus on the properties of fuels that characterize the fuel susceptibility to knocking (octane number) or the so-called hard running of the engine (cetane number and cetane index). In the article, we present for which fuels these properties are monitored, what are the limit values of these parameters and what are the reasons for their monitoring. We also present the testing methods that are used to determine these properties.