Keeping the intake valve open past BDC, as the piston starts to rise, effectively lowers the compression ratio at low engine speeds to prevent detonation (knocking) and results in raising it at higher speeds when more horsepower is sought. Step 1 : calculate the mass flow rate The compressor is to deliver 2000 Nm3/h of air. For air, this factor is about 1.4:1. Resistance factor is defined as the ratio of measured pressure drop across a compressor valve to the pressure drop that would be predicted in flowing the same quantity of the same gas at identical upstream pressure and temperature conditions through a round hole (an orifice) having a discharge coefficient equal to one and an area equal to the valve pocket opening. For a day at standard atmospheric conditions. 17.9.The figure also shows the trend in the maximum to minimum cycle temperature ratio, T 3 /T 1.It has been stated that the increase in specific work results in an increase in turbine entry temperature, T 3.Since the ambient temperature, thus the compressor inlet temperature, T 1, is constant, T 3 /T 1 will increase. Per Wikipedia: If the nominal compression ratio of an engine is given, the pre-ignition cylinder pressure can be estimated using the following relationship: where is the cylinder pressure at bottom dead center (BDC) which is usually at 1 atm, is the compression ratio, and is the specific heat ratio for the working fluid, which is about 1.4 for air, and 1.3 for methane-air mixture. Compression Ratio. I find out inter stage pressure based on formula P i =(P 4 /P 1) (1/n) For Example : P4=650 psia. It is important to use units of Absolute Pressure for both P1c and P2c. Gauge Pressure (in units of psig, the g refers to “gauge”) measures the pressure above atmospheric, so a gauge pressure reading at atmospheric conditions will read zero. The efficiency of the compressor is known and is 0.72. Compression ratio calculation. Where: = Pressure Ratio. P 1c = Compressor Inlet Pressure. She holds a bachelor's degree in language arts and a Master of Education degree. For the actual gas flow rate at the inlet condition, the polytropic efficiency is close to the compressor best efficiency point (BEP). Compression ratio (R) – is the pressure ratio at discharge to suction pressure: R = Pd/Ps (where Pd and Ps are absolute). But in actual case pressure ratio (P i) at each stage will be different. Pressure ratio. Compression ratio and overall pressure ratio are interrelated as follows (what follows is valid only for static pressures, not overall pressure ratios, as compression while slowing down flow without doing work is not changing stagnation pressure at all, and in supersonic flow with shock waves stagnation pressure will be less than 1 with > 1 compression ratio): Boost gauges measure the manifold pressure relative to atmospheric pressure, and thus are measuring Gauge Pressure. Calculate basic compression pressure from the two low- and high-speed effective compression ratios of 7.32:1 and 8.55:1, respectively, assuming standard sea-level atmospheric pressure of 14.7 pounds per square inch absolute (psi). When the air is compressed, some of its heat is extracted because of its lower volume, but it has nowhere to go, so the heat results in a higher temperature, which in turn increases the pressure above what it would have been under ideal conditions. This calculation is based on the definition of the pressure coefficient and the definition of the polytropic work. Above calculation is correct for ideal case. n( No of stages)= 4. Calculate basic compression pressure from the two low- and high-speed effective compression ratios of 7.32:1 and 8.55:1, respectively, assuming standard sea-level atmospheric pressure of 14.7 pounds per square inch absolute (psi). P 2c = Compressor Discharge Pressure. 12 psig + 14.7 psia = 26.7 psi absolute pressure in the manifold, 14.7psia – 1 psig = 13.7 psia at compressor inlet, (12 psig + 12.4 psia) / (12.4 psia – 1 psig) =, EMAIL: SALES@TURBOWORX.COM | PHONE: 667-212-4975. In that chart that accompanies part one of this series, the left side (Y-axis) represents compression ratios. The high-speed value … The efficiency of the compressor is known and is 0.72. : R2 = Pd/Pi At higher elevations, this can have a significant effect on pressure ratio. 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