Power plants FG WILSON
Engine exhaust
Engine exhaust must be directed outwards through a properly designed exhaust system that does not create excessive back pressure for the engine. A suitable muffler must be included in the exhaust line. Elements of the exhaust system, which are located inside the generator room, must be insulated to reduce heat radiation. The open end of the pipe must be equipped with a visor to protect against rain or snow entering the exhaust system (or cut at an angle of 60a to the horizontal). If the building has a smoke detection system, the exhaust pipe must be located so as not to trigger the system.
Exhaust
To ensure the economy of the installation and the efficiency of operation, the location of the engine should be such that the exhaust pipe has as few bends and narrowing as possible. Usually, the exhaust pipe is led outside the wall of the building and rises to the roof. In the hole in the wall, there should be a sleeve for absorbing vibrations, as well as a thermal expansion compensator. (Figure 6.1.)
It is not recommended to combine the exhaust of the engine with the chimney of furnaces or other equipment, as there is a danger of back pressure, which disrupts the functioning of other devices. Similar use of a chimney for several devices is permissible only if there is no deterioration of the engine characteristics or other equipment allows the use of a common chimney.
The exhaust can be directed into a special shaft, which also serves as an air outlet that passes through the radiator and can have sound insulation. The air that has passed the radiator is fed below the exhaust so that the outgoing air mixes with the exhaust gases. See Figures 6.2 and 6.3. The muffler can be located inside the mine or in a room with an exhaust pipe extension leading out through the mine. Vanes should be installed in the shaft to direct the air flow upwards and reduce the flow restriction of the radiator fan. A curved contour with a sound-absorbing coating can also be used to direct the flow upwards. For a generator set installed in a roof extension, a separate enclosure or on a trailer, the exhaust and radiator outlet may be combined above the enclosure without a shaft. Sometimes for this, the radiator is installed horizontally, and the fan is driven by an electric motor to obtain a vertical flow of air.
Figure 6.1. A typical release system installation
Figure 6.2. Horizontally installed muffler. The exhaust pipe and the radiator air flow pass in one shaft
Figure 6.3. The air of the radiator passes through a shaft with sound insulation. A muffler is installed in the same mine
Flexible section of the exhaust pipe
A flexible section between the nozzle and the exhaust piping must be used to prevent the transmission of vibration from the engine to the piping and building, and to isolate the engine and piping from forces resulting from thermal expansion, displacement, or the weight of the piping itself. The design of the flexible section shall permit continuous removal of ± 13 mm (0.5 in.) of either end in any direction without damage. The section must not only be flexible enough to compensate for the nominal value of the constant displacement between the pipeline and the nozzle, but also be easy to spring during the rhythmic oscillations of the generator set on shock absorbers due to load changes. The flexible coupler must be ordered together with the genset.
Exhaust pipe insulation
Open parts of the exhaust system must not be near wood or other combustible materials. The indoor exhaust pipe and silencer, if also installed indoors, should be jacketed with suitable insulating material to protect personnel and reduce room temperature. A sufficient layer of suitable insulating material wrapped around the muffler and piping, and secured by a stainless steel or aluminum jacket, can significantly reduce the amount of heat radiated into the room from the exhaust system.
Minimization of exhaust gas flow restriction
The free passage of exhaust gases through the pipe is the basis for minimizing exhaust back pressure. Excessive exhaust back pressure significantly affects engine power, durability and fuel consumption. The resistance to exhaust gases from the cylinder causes incomplete combustion of fuel and an increase in operating temperature. The main design factors that can cause back pressure are:
- The diameter of the exhaust pipe is too small
- The length of the exhaust pipe is too long
- Too many sharp bends in the exhaust system
- Muffler resistance is too high
- At some critical length values, standing waves can cause high back pressure
Excessive drag in the exhaust system can be avoided by choosing the right design. To ensure that there are no problems related to excessive resistance, arrange with your F.G. Wilson distributor to check your design.
The effect of pipe diameter, length and bend resistance can be calculated to ensure that your system does not have excessive back pressure. The longer the pipe and the more bends it has, the larger the pipe diameter is needed. The amount of back pressure must be calculated at the installation stage to ensure that it will be within the recommended limits for the engine.
Measure the length of the exhaust pipe based on your installation diagram (Figure 6.4.) Take the value of the exhaust gas flow rate and the value of the back pressure limits from the tables of the technical characteristics of the generator set. Substituting the muffler resistance value and the number of bends, calculate the minimum diameter of the pipe. This value should not exceed the recommended exhaust back pressure limits. It is also necessary to take into account the deterioration of the characteristics and the accumulation of soot, which can increase the resistance.
The resistance of bends is the most convenient value when calculating the length of the straight equivalent section of the pipe for each bend and summing it with the total length of the pipe. For bends and flexible sections, the equivalent length of a straight pipe section is calculated as follows:
45° bend: Length (feet) = 0.75 × Diameter (inches)
90° bend: Length (feet) = 1.33 × Diameter (inches)
Flexible Sections: Length (ft) = 0.167 × Diameter (in)
The following formula is used to calculate the back pressure of the exhaust system:
Р = CLRQ2 ÷ D5
where:
P = the value of the reverse mercury column in inches
| С = | 0.00059 with air consumption from 100 to 400 cubic meters. ft/min to burn fuel |
| 0.00056 with air consumption from 400 to 700 cubic meters. ft/min to burn fuel | |
| 0.00049 with air consumption from 700 to 2000 cubic meters. ft/min to burn fuel | |
| 0.00044 with air consumption from 2000 to 5400 cubic meters. ft/min to burn fuel |
L = length of exhaust pipe in feet
R = Exhaust Density in lbs/cu.ft, R = 41.1 ÷ (Exhaust Temp áF + 460 áF)
Q = exhaust gas flow in ft/min*
D = inside diameter of exhaust pipe in inches
* Taken from the table of technical characteristics of the engine
This formula is valid under the assumption that the exhaust pipe is made of grade steel or ductile iron. The amount of back pressure depends on the cleanliness of the pipe surface and increases with the increase of its roughness. The value of constant 41.1 is based on the mass of air required for fuel combustion at rated load under the conditions specified by the SAE standard. For values of exhaust gas temperature and air flow, see the table of technical characteristics of the engine. Conversion tables to other units of measurement are given in the Glossary.
