The role and importance of fuels in the economy have changed significantly because of scientific and technological revolution. It was caused by the following features:
- Fuel consumption has risen sharply, and the excessive requirements for its quality even on individual parameters lead to significant expenditures in the production; at the same time the use of understated quality products causes multi-million losses for the organizations that use machinery and equipment;
- There has been a need for the new systems and methods, including accelerated fuel test, as well as the development and implementation of advanced grades require long-term studies, which becomes an obstacle in creating the new technology;
- There are new demands for the quality of fuels and lubricants in addition to existing ones, which depend not only on technology but also on energy, technological, economic, and environmental requirements and the conditions of foreign and national specifications for fuels and lubricants;
- The problems of quality and rational use of fuel have gained cross-industry value because of their increased role in quality issues for increasing the reliability, durability and economy of technology.
The factors determining the safety of flight primarily include those associated with the reliability of the aircraft in flight, for example, the reliability of structural components and systems. When considering the impact of fuel properties on a flight safety, the fuel must be regarded as a constructive part of the aircraft (helicopter) and the engine, therefore, the fuel must be trustworthy, reliable, and efficient. Consequently, the impact of properties of fuels and lubricants on the safety of a flight is shown through their effect on the reliability of systems and an engine.
The fuel may be the cause of such accidents as:
- engine failure,
- drop of its thrust,
- and fire in the engine.
Engine failure in flight may be caused by the termination of the fuel supply into the combustion chamber or the destruction of the turbine. The same happens with complete blockage of filter pores by ice crystals or other low-temperature deposits, and high-pressure pump failure because of poor anti-wear properties, etc.
The reason for the fall of the engine thrust may be reducing the fuel supply, caused by partial blockage of the filter screens by high-temperature or the low-temperature deposits, a significant increase in fuel viscosity, the formation of gas bubbles in the fuel, and by cavitation in the fuel system.
The fire in the engine during a flight is possible due to a disorder in fuel spraying by fuel injectors, which can be caused by deposits, burnout of the combustion chamber, etc.
Fuel properties, having a direct influence on the appearance of emergencies can be grouped by having their effect on reliability of:
- the fuel pump (antiwear, corrosivity, admixtures content);
- the fuel system in high altitude conditions (volatility, viscosity, water and resinous compounds contents, crystallization of the fuel, its thermal stability, etc.);
- and of the combustion chambers and nozzles (tendency to deposit formation, thermal stability).
Since there is no relevant statistical information on the engine failure in flight caused by fuels and lubricants, it is not possible to talk about the quantitative impact of their individual properties on flight safety. It should be noted that aviation transport belongs to such a kind, in which the occurrence of failure immediately leads to a response – establishing the cause and its immediate elimination.
When a failure occurs because of poor fuel properties, the cause of its appearance is identified and eliminated. This is evidenced by a solid experience of fuel usage. In the late 1940s and early 1950s flight accidents in the operation of domestic aircraft with air-breathing jet engine began to emerge. They were caused by water being abundantly present in the fuel. In order to remove it, the fuel systems of aircrafts have been improved, strict regulations on the content of free water in the fuel supplied to the fueling have been introduced, the methods of dehydration of fuel using filter-water separators have been developed, and special additives have been introduced. Implementation of these measures increased the flight safety.
In the mid-1950s flight accidents were caused by the failures of high pressure pumps due to severe corrosion when operating on fuels derived from sulfurous crude oils. In order to eliminate these faults as for the content of corrosive compounds in fuels, the requirements were tightened, and also a number of technological and constructive activities were done.
In the early 1960s when operating aircraft with gas turbine engines, failures of aggregates of engine fuel system in flight appeared. The reason for this was in atmospheric precipitations clogging filters and the deposits. This led to a tightening of fuel requirements in terms of the content of aromatic hydrocarbons, resinous compounds, reduced pour point, increased oxidative stability, as well as improving the injectors, combustion chambers and the combustion process control. In the mid-1960s, following the introduction of hydrotreated fuels, failures of high pressure pumps because of poor anti-wear properties were observed. This flaw has been eliminated by improving the design of pumps and the introduction of hydrotreated fuel RT with an antiwear additive. In the late 1960s and early 1970s the cause for active filter plugging was in a formation of low-temperature deposits consisting of soaps of naphthenic acids. These were eliminated by improving the fuel cleaning and removal of alkaline treatment in the production of fuel.
Flight safety is largely determined by the reliability of the engine and fuel system of an aircraft, which, in turn, depends on fuel properties. Achieving a high level of reliability at the present stage of technological development based on economic factors and energy problems can only be a result of a rational combination of the characteristics of technology, operating conditions and fuel properties.
The high level of flight safety achieved to date is a testament of effective work on improving the design of aircrafts (helicopters) and the work of civil aviation organizations to provide the flights with quality fuels and lubricants. One of the pressing issues of ensuring the safety of aircraft (helicopters) flights is the creation of the automatic quality control system of fuels and lubricants directly at the fuel filling stations.