Orlando Volpato, Delphi - AEA – Associação Brasileira de ...

The ethanol is injected into the inlet air and mixed with air. As diesel fuel enters the
combustion chamber due to the pilot injection; it is ignited by the hot air after a very
short delay, creating many ignition fronts to burn the natural gas mixed with air.
In figure 13 a photograph of a diesel fuel injection being ignited by the hot air is
shown to illustrate the pilot injection concept. The injector in the example has 6 holes.
The diesel-ethanol engine is possible because the auto-ignition temperature of
ethanol is higher than the temperatures at the end of compression cycle [37].
A diagram with the temperature in the air inside the cylinder in function of crankshaft
angle is presented in figure 14. The temperature was calculated using the expression
Tc = To * r (n-1), where r is the compression rate (r = 16.8) and n is the polytrophic
exponent for real gases (n = 1.35) [26].
The line with 130 degC intake temperature indicates the limit of operation without
auto-ignition issues.
For a compression ignition engine, using a mechanical diesel fuel injection system,
where the fuel is injected in one event, there are two combustion phases, as
exemplified in figure 15.
The injected fuel does not burn instantaneously, it takes a time to vaporize the fuel
and to chemical reactions to take place and release energy into the combustion
chamber.
Fig. 13: Internal view of cylinder after some milliseconds of diesel fuel injection
This term is called “ignition delay” and after that time most of the fuel already injected
burns in a short period. This is termed “pre-mixed combustion phase”.
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