Dual-Fuel Diesel engines
The rate of consumption of the energy resources available continues to increase in spite of the significant progress being made to enhance the efficiency of their usage. Contributions to this increase in consumption include the rise in world population, improvements in the average standard of living, and the increase in average life
expectancy. It is expected that the combustion of fossil fuels will continue to be the prime source to rely on for energy for some time to come. This will be constrained, however, by the continued depletion of crude petroleum resources of quality, the need for ever-cleaner exhaust emissions, and the rapid progress being made in the development of renewable resources. On the other hand, it is becoming increasingly evident, especially more recently, that the availability of natural gas, as well as other
gaseous fuels, is increasing. This has come about mainly as a result of the improve-ments in the long-range transportation of gas and the increased availability of uncon-ventional sources, such as those of shale gas, biogases, and coal bed–derived gases. Moreover, the increased exploitation of unconventional resources of liquid hydro-
carbon fuels, such as tar sands, is bringing with it the potential production of large amounts of gaseous fuel mixtures, albeit of varied quality and having lower heating values than those of the conventional processed pipeline natural gas. On this basis, there are many opportunities to increasingly exploit such gaseous fuel resources while at the same time economizing on the consumption of other nonrenewable type liquid fossil fuel resources. Such approaches would need to develop further new means for the production of power while continuing the overall reduction of exhaust emissions, including those associated with their contribution to global warming.Much benefit has been derived from the continuing investment in research and development directed at supporting and improving the performance of the wide variety of power-producing devices of the internal combustion type. These have progressed rapidly over the years to a current level where high-quality performance is achieved with reliability while spanning a wide diversity of designs, sizes, and fields of application. In recent decades in particular, reciprocating internal combus-
tion engines became the dominant versatile and convenient form of power genera-tion systems, including at the individual consumer level. Moreover, the diesel engine, especially through the rapid progress made in recent years, has come to be recognized as the prime class of combustion engines for the economic production of power, for both stationary and mobile applications. The modern diesel engine nowadays is of a superbly high efficiency, combined with very high specific power output and excellent
reliability and durability, and favorable output torque and exhaust emission charac-teristics. The conventional diesel engine is distinguished additionally by its ability to be developed in widely different sizes and ranges of power output. These can vary by orders of magnitude, from those producing merely a few kilowatts to those capable of producing several thousands of kilowatts per engine cylinder. A wide spectrum of fields of application that spans small sizes such as those powering lawn mowers huge ones that may power a super-tanker or provide the main electrical energy supply
to a small town is also covered.An important positive feature of the compression ignition engine of the diesel type, by virtue of its mode of combustion, is its tolerance to accept a wider variation in the fuel type used, more so than the spark ignition engine. Historically, diesel engine applications have employed a wide range of fuels that include not only those that are liquid, but also those that are gaseous. On this basis, the usage of diesel engines will continue to increase, benefiting from the improvements in performance, economy, emissions, and reliability. Moreover, this type of engine probably will continue to command the major sector of power generation via internal combustion prime movers, aided by the inherent capacity of the diesel engine to relatively easily
tolerate changes in the type of fuel employed, including those fuels derived directly
or indirectly from biosources or from the processing of natural gas.
It is also evident that there is a need to develop approaches to the production of power that capitalize on the relative superiority of the diesel engine as a power producer, in comparison to other prime movers, while exploiting the increasingly
available reserves of natural and other fuel gases. At the same time, this will reduce the consumption of the depleting reserves of liquid petroleum fuels in general, and in particular those associated with the high-quality liquid fuels recently required for diesel engine operation. Accordingly, these requirements point to the gas-fueled die-sel engine, commonly known as the dual-fuel engine, as the most favorable device to employ. The future of such applications appears to be very promising, supported by the rapid technical advances made in recent years that lead to the superior optimiza-
tion of their operation and control.
Engines that operate in the dual-fuel mode are normally conventional diesel engines converted so as to be capable of burning a gaseous fuel while using the conventional liquid fuel injection system of the engine to introduce only a relatively
small amount of liquid diesel fuel to provide consistent ignition. These engines that require a minimum of modification from the diesel version can be operated to con-
sume a relatively wide range of gaseous fuels while often retaining the full capacity to operate whenever desired as a conventional diesel engine. They economically
produce power at high thermal efficiencies that can exceed those of diesel engines,
with favorable levels of exhaust emissions and reliability.
The objective of the present contribution is to present to engineering students, practicing engineers, technologists, and scientists at all levels a comprehensive and
well-integrated review of the relevant fundamentals and practices of the operation of gas-fueled diesel engines of the dual-fuel type in their variety of sizes and fields
of applications. Both the positive features and limitations are highlighted, together with an outline of measures for optimizing their operation and overcoming some of their apparent potential limitations. The latest developments in this rapidly expand-
ing field, especially for the transportation sector, are reviewed, together with a dis-cussion of possible future development in this economically and environmentally
important field.
To download klick here