As a field power source and emergency power reserve, diesel generator sets are widely used in industrial and agricultural production, national defense, science and technology and daily life. So as a buyer, how to buy a satisfactory diesel generator set?
Generally speaking, the performance of diesel generator can be measured by the following four technical indexes: power performance index, exhaust pollution index, economy index, weight and shape size index, etc.
The economic index generally refers to the fuel consumption rate and the lubricating oil consumption rate of the diesel engine.
1. specific fuel consumption
Fuel consumption rate for short fuel consumption rate, it is the diesel engine per kilowatt-hour consumption of fuel A in g / (kWh). The fuel consumption rate per kilowatt-hour in an indicator power meter is called the indicative fuel consumption rate, and the fuel consumption rate per kilowatt hour in an effective power meter is called the effective fuel consumption rate. The former indicates the indicator of diesel engine economy. The latter indicates the economic efficiency of a certain engine. The fuel consumption rate referred to in the diesel engine product description refers to the effective fuel consumption rate. After measuring torque Me and rotational speed n, as well as fuel consumption per hour tGt (kg/h) and effective power Pe, the effective fuel consumption rate (ge,) is obtained by using the following formula.
ge=Gt/Pe*10^3[g/(kW.h)]
The range of ge [g / (kW.h)] for diesel engines is as follows:
High speed diesel engine, ge=212~235; low speed diesel engine, ge=169~190.
2. specific lubricating oil consumption
When the diesel engine is calibrated, the g per kilowatt-hour oil consumption of diesel engine is called the skid consumption rate in g / (kW h).
Diesel engine lubricating oil is used continuously in the engine, the main reasons for its consumption are: the diesel engine oil in operation through the piston into the combustion chamber or by the valve pipe flow in the gas cylinder burned, not burned with the exhaust gas discharged; In addition, a portion of the lubricating oil due to atomization or evaporation in the crankcase by the crankcase vent. Diesel engine oil consumption rate is generally 0. 0. 5-4g/ (kW.h) is about.
The power performance index refers to the external work capacity of diesel engine, generally refers to the power, the average effective pressure, the rotational speed and the piston average speed and so on.
1. active power
The power of a diesel engine in unit time in kW,1kW=1000N. M/s.
The work done by a diesel engine per unit time in the cylinder is called indicated power. The power extracted from the engine crankshaft is called effective power Pe. after the indicated power is subtracted from the friction loss of the internal parts, the mechanical loss power such as the pump air torsion loss and the control accessory wrench is subtracted from the engine crankshaft.
If the engine crankshaft's speed per minute is n, the crankshaft's effective power output per second is We,. Because of We=2*PI*n/60*Me (N. m), the effective power of diesel generator is Me-- effective torque in Pe=PI*nMe/30000 (kW).
2. Speed and piston average speed
A. Speed diesel engine crankshaft per minute speed, expressed in r/min. The speed has great influence on the performance and structure of diesel engine, and its range is very wide. Various types of diesel engine speed range is different.
B. The average speed of the piston Cm piston is constantly changing in the cylinder, which is larger in the middle of the stroke, smaller in the vicinity of the stop point, and zero at the stop point. If the engine speed n is known, the piston average velocity can be calculated by the lower formula
Cm=2*Sn/60=Sn/30 (m / s). S- stroke
3. mean effective pressure
The average effective pressure of eight is usually used to compare and evaluate the dynamic performance of various engines. It is a hypothetical pressure acting on the top of the piston, and it is the work done by the piston to move a stroke, equal to the effective work done per cycle.
The effective power can also be expressed with the following expression
Pe = i * Vs * Pe * n/ 30t (kW)
Where i - the number of cylinders;
Vs-cylinder working volume, L;
Pe—average effective pressure, MPa;
n — engine speed, r / min;
t The number of strokes of an engine, t=4 for a four-stroke engine and t=2 for a two-stroke engine.
Then Pe=30*t*Pe/i*Vs*n
It can be seen that Pe represents the effective power per unit cylinder working volume. Pe is an important index. It not only indicates the working cycle is good or bad, but also includes the size of mechanical loss. Under the same conditions, the higher the Pe value is, The more effective work the engine outputs, the value of the Pe is generally as follows:
The non-supercharged diesel engine is (0. 5—O.9)MPa
The supercharged diesel engine is (0. 8—3.2)MPa.
There is a small but very harmful amount of emissions in the exhaust of diesel generator sets. They are carbon monoxide, CO, hydrocarbons, HC, nitrogen oxide, NO, and sulfur dioxide, SO2.. These combustion products pollute the environment and are harmful to human health, resulting in social pollution.
With the enhancement of environmental protection consciousness, the restriction of diesel engine exhaust pollution is becoming more and more strict. China's national standards (GB 267-87) have imposed NO II limits on diesel engine emissions as follows:
When Pe>300 kPa, the NOx limit is 29 g/(kW·h) at ge “214 g/(kW·h);
When g, = 214-268g / (kW .h), the NOx limit is 14-25g (kW · h);
When ge>268g/(kW·h), the NOx limit is llg/(kW·h).
The weight and overall dimensions of the diesel engine are an index to evaluate the structure of the diesel engine and the utilization of the metal material. the requirements for weight and overall dimensions of various types of diesel engines are different.
gw=Gw/Pe(kg/kW)
The so-called net weight refers to the quality of the auxiliary equipment and auxiliary systems which do not include fuel oil, lubricating oil, cooling water and other auxiliary systems not directly installed on the internal combustion engine body.
The specific mass is related not only to the type of diesel engine, the structure, the size of accessories, but also to the materials used and manufacturing technology.
3. Shape dimension index
Shape dimension index, also called compactness index, is the index of compact degree of overall arrangement of diesel engine. It is usually measured by the unit volume power of a diesel engine.
The unit volume power Pv is the ratio of the calibrated power Pe of the diesel engine to the external volume V of the diesel engine.
Pv=Pe/V (kW/m^3)
The L, B, H is the maximum length, width and size of the diesel engine.
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