The mechanism of the action of oxygenates is discussed from the standpoint of redox reactions. It is shown that the action of oxygenates on the process of combustion of hydrocarbons is associated with oxidation of the latter in steps. The reason for the increase in octane number upon addition of oxygenates may be different rate of overcoming conformational differences under conditions close to the critical temperature of the hydrocarbon at the pre-ignition combustion stage. The influence of propylene oxide on the performance properties of gasoline is examined.The development of chemmotology presupposes study of the mechanism of the action of various hydrocarbon fuel additives and dopes at the stages of production, storage, and use of the fuel. This relates primarily to oxygenate additives, which are used in millions of tons. It is established experimentally that these additives raise the octane number of gasoline, but the mechanism of their action is not fully clear.For gasoline, mainly single-atom alcohols, ketones, and ethers are used as oxygenates. The content of these oxygenates in terms of oxygen does not exceed 3%. Further rise of their content becomes ineffectual. Of these compounds, the most easily available are ethanol and methanol. Ethanol as a gasoline additive is known since late 19 th century. This alcohol was treated as an "alternative" fuel with a special focus on its strength (water content) and ability to form homogeneous solution with gasoline at low temperatures. Widely used were fuel blends with absolute ethanol with a concentration of up to 99.99 wt. %. With switch over to methanol, stabilization of the blends became complicated.High alcohol content makes ignition of the fuel difficult, so alcohols began to be substituted by ethers, which are highly volatile and ignite at a low temperature. Among the ethers, the most popular in Russia and abroad is methyl-tert-butyl ether. Its production and use in the world in 2001 comprised 26.5 million tons [1].The rise of octane number of alcohols in the sequence C 8 -C 4 -C 1 can be associated with increase in the relative proportion of oxygen in their molecule. This agrees well with reduced knocking under the action of water, in the molecule of which the relative proportion of oxygen is the maximum. As is well known, alcohols and alcohol-gasoline blends are poorly susceptible to tetraethyl lead additive, which may mean different mechanisms of action of these additives [2].

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The melting (crystallization), separation, and boiling points of a mixture of propylene oxide and water were determined and used to plot the phase diagram of the mixture. The composition of propylene oxide crystal hydrate was investigated. The triangular diagram of separation of the system at 20°C was plotted with the results of studying the mutual solubility in the ternary straight-run naphtha -propylene oxide -water system. Key words: ternary straight-run naphtha-propylene oxide-water system, solubility in ternary system, propylene oxide crystal hydrates.Due to the prohibition of use of organometallic compounds [1], oxygenates are the most important octaneboosting additives to motor fuels: ethanol, isopropanol, tert-butanol, isobutanol, C 5 ethers, etc. Propylene oxide (PO) has been examined as another oxygenate [2][3][4]. The mechanism of action of oxygenates, including propylene oxide, was proposed in [5]. The physicochemical and performance characteristics of composite fuels must be investigated for incorporating oxygenate compositions with propylene oxide.We investigated the mutual solubility in the straight-run naphtha-propylene oxide-water (SN-PO-water) ternary system and plotted the solubility diagrams. In the first stage, we studied the PO-water binary mixture. The melting (crystallization), and boiling (GOST 18995.5-73) points, and separation point of the mixture were determined [6]. The PO content in the binary and ternary mixtures were determined by a chemical method based on the reaction with HCl [7].The melting (crystallization, separation, and boiling points of the PO-water mixture coincide. The phase diagram of the system was plotted for better understanding of the results obtained (Fig. 1). The region of separation of this mixture can arbitrarily be divided into three parts. In the first and third parts, the separation and melting (crystallization) points coincide, while they differ in the second part, but the boiling point coincides with the separation point in this part. It is characteristic for the melting point of the PO-water mixture to decrease sharply in the third part for a PO content above 95 wt. %.The phase diagram shows that sediment stably precipitates in a wide range of PO contents at -6.5°C. This sediment is a white, crystalline substance which was separated on a filter at the temperature of -10 to -21°C. The melting points

The flash point is one of the most important characteristics used to assess the ignition hazard of mixtures of flammable liquids. To determine the flash points of mixtures of secondary alcohols with n-alkanes, it is necessary to calculate the activity coefficients. In this paper, we use a model that allows us to obtain enthalpy of fusion and enthalpy of vaporization data of the pure components to calculate the liquid-solid equilibrium (LSE) and vapor-liquid equilibrium (VLE). Enthalpy of fusion and enthalpy of vaporization data of secondary alcohols in the literature are limited; thus, the prediction of these characteristics was performed using the method of thermodynamic similarity. Additionally, the empirical models provided the critical temperatures and boiling temperatures of the secondary alcohols. The modeled melting enthalpy and enthalpy of vaporization as well as the calculated LSE and VLE flash points were determined for the secondary alcohol and n-alkane mixtures.

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