Airplane Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 145

Chapter 10
Airplane Engines
Aircraft engines operate with reciprocating, i.e. a four-stroke internal combustion
engines or with gas turbines. Gas turbines, operating continuously and using the
principle of the Brayton-cycle, have gained a leading position in the last 50 years.
Most modern airliners use gas turbines in jet engines, fly faster and at higher
altitudes than reciprocating engine and propeller driven airplanes [ 1 ].
The thrust depends on the mass of air moved, mixed with the exhaust gas in the
core and with the air in the by-pass. Propellers and gas turbines' blades are flow
machines to move airplanes, similarly to ships in water, through rotating and
creating thrust in the air. Propeller engines have higher efficiency and lower fuel
consumption than jet engines since they move a large air mass at a slower speed in
opposite to jet engines which move a small air mass flow at high speed.
The gas turbine in a modern jet engine produces usually low concentrations of
pollutants in the combustion chamber (see Fig. 10.1 )[ 2 ].
However, the real proportions are very different in airplanes depending on
type, age, and maintenance of airplanes. Beside the high efficiency and the low
concentration level, the general problems arise from the high mass flow of burning
substances and the high altitude of the emissions. Cold temperatures and low
density of ambient air in higher altitudes lead to long decomposition time intervals
of the substances emitted [ 3 ].
10.1 Types of Engines
The most important types of aircraft engines are the turbojet, the turboprop, the
turbofan and the turboshaft engine type. Turbojet is the oldest kind of general
purpose jet engine. Currently, the most important system is the turbofan tech-
nology. The main parameters of types are presented in Table 10.1 .