Cylinder Combustion Process of Cummins Generator
by Starlight Generator dieselgeneratortechAccording to the
characteristics of variation of gas pressure and temperature in cylinder, the
combustion process of Cummins diesel generator generally can be divided into
four stages: delayed combustion period, rapid combustion period, slow
combustion period and after combustion period. In these four stages, the
specific performance of each combustion stage is different.
Here we take everyone to
understand the performance of each combustion stage, so as to help users figure
out what kind of working status of the diesel generator set is in.
1.Delayed
combustion period.
From the beginning of
oil injection to ignition is called delayed combustion period. This is the
physical preparation of the injected fuel for atomization, heating,
evaporation, diffusion, mixing with air, etc. In generally, the delayed
combustion period is 0.0007~0.003s.
Delayed combustion
period has a great impact on the operation of diesel engines. The longer this
period, the more fuel is injected into the combustion chamber, the faster the
pressure in the cylinder rises. Although this can slightly improve the economy,
but it increases the roughness of the engine work and accelerates the wear and
tear of the machine. Therefore, the general diesel engine would rather
sacrifice some economy, but also let its work smoothly.
The main impact factor
of delayed combustion period is the quality of diesel fuel, temperature and
pressure at the end of compression and air vortex in combustor etc..
2.Rapid
combustion period.
The period from the
start of fuel ignition to the moment of rapid combustion and the highest
pressure is called the rapid combustion period. The characteristics of the
period is high heat release rate (dQ/dч), fast increase of pressure and
temperature in cylinder. Its pressure rise rate depends on the quantity of
combustible gas mixture which formed during delayed combustion period. In order
to let diesel engine stable work, max. pressure rise rate (dQ/dч) should be not more
than 0.40~0.60MPa/℃A.
3.Slow
combustion period.
The slow-burning period
is the period from the highest pressure to the highest temperature. The
characteristic of this period is that the combustion is carried out under the
condition that the cylinder volume is increasing, which is mainly controlled by
the formation speed of the mixed gas, and the burning speed is slower than the
rapid burning period, The gas temperature rose to a maximum of 1973~2273K, but
the pressure dropped slightly. At the end of the slow-burning period, the
amount of heat released generally reaches 70% to 80% of the total heat of
circulation.
4.After
combustion period.
The after combustion
period is a period from the highest temperature point to the end of combustion.
This period is characterized by burning on the expansion line. At this time,
the oxygen is greatly reduced, the heat release rate is lowered, and the heat
released by the fuel cannot be effectively utilized, thereby increasing the
exhaust gas temperature and reducing the economy. At the end of after
combustion, the heat release rate has reached 96%~98% of the total circulation
heat release rate. The higher the speed of diesel engine, the longer the after
combustion period.
The burning speed of
after combustion period is very slow, and the piston has been far from the top
dead point, the capacity of cylinder has increased too much, at this time, the
temperature and pressure in the cylinder are rapidly declining. Therefore, the
heat released during the after combustion period is not only difficult to use,
but also increases the heat load of the parts, increases the exhaust temperature,
increases the cooling heat loss, and reduces the economic efficiency of the
diesel engine. Therefore, the shorter the after burning period is the better.
The main factors
affecting combustion process are structural factors and operational factors.
The main structural factors are compression ratio, combustion chamber, intake
port, structure form of fuel injection pump and injector, and injection law,
etc. The main operating factors are diesel oil performance, injection advance
angle, injection pressure, load and speed etc.
In order to improve the
formation conditions of combustible mixture gases, reasonable combustion is
adopted to shorten the after combustion period and improve the economy of
diesel engines. Generally, high compression ratio (15-20) is adopted in diesel
engines. At the same time, strong air movement is carried out in the combustion
chamber, and the fuel injection law of first priority and then urgency is
adopted, to ensure high enough injection pressure (usually above 10 MPa), and
select diesel Oil with higher fuel cetane value.
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Created on Nov 4th 2019 01:37. Viewed 294 times.