Mean effective pressure

Fig. 7. NO formation for the Provo-Orem bus mn at a compression ratio of 12 1 at 30°C, 3000 rpm, where A is brake mean effective pressure B, brake thermal efficiency and C, oxides of nitrogen, (a) Effect of equivalence ratio, ( ), at a water/H2 mass ratio of 6.0 and spark = 17° before top-dead (BTC) and (b), effect of water injection where (j) = 0.60 and spark = 14°BTC. To convert MPa to psi, multiply by 14.

The power of the engine is expressed by die mean effective pressure, mep, where... 

In practice the clamping pressure will also depend on the geometry of the cavity. In particular the flow ratio (flow length/channel lateral dimension) is important. Fig. 4.42 illustrates typical variations in the Mean Effective Pressure in the cavity for different thicknesses and flow ratios. The data used here is typical for easy flow materials such as polyethylene, polypropylene and polystyrene. To calculate the clamp force, simply multiply the appropriate Mean Effective Pressure by the projected area of the moulding. In practice it is... 

The thickness of the moulding is 1 mm, hence the flow ratio = 150/1 = 150. From Fig. 4.42 at this thickness and flow ratio, the mean effective pressure is 75 MN/m. ... 

Assuming that the mean effective pressure also applies to the runner system, then... 

This is also the flow ratio, so from Fig. 4.42 the mean effective pressure is 50 MN/m. Applying the viscosity factor, etc as above, then... 

It may be seen from the above analysis and that in Chapter 4 for the calculation of clamping force on an injection moulding machine the Mean Effective pressure (MEP) across the cavity may be obtained from... 

One way to simplify the calculation of the net work of the cycle and to provide a comparative measure of the performance of an Otto heat engine is to introduce the concept of the mean effective pressure. The mean effective pressure (MEP) is the average pressure of the cycle. The net work of the cycle is equal to the mean effective pressure multiplied by the displacement volume of the cylinder. That is,... 

An ideal Otto Cycle with air as the working fluid has a compression ratio of 9. At the beginning of the compression process, the air is at 290 K and 90kPa. The peak temperature in the cycle is 1800 K. Determine (a) the pressure and temperature at the end of the expansion process (power stroke), (b) the heat per unit mass added in kJ/kg during the combustion process, (c) net work, (d) thermal efficiency of the cycle, and (e) mean effective pressure in kPa. 

An ideal Diesel engine receives air at 103.4 kPa and 27°C. Heat added to the air is 1016.6 kJ/kg, and the compression ratio of the engine is 13. Determine (a) the work added during the compression process, (b) the cut-off ratio, (c) the work done during the expansion process, (d) the heat removed from the air during the cooling process, (e) the MEP (mean effective pressure), and (f) the thermal efficiency of the cycle. 

A Diesel cycle has a compression ratio of 18. Air-intake conditions (prior to compression) are 72°F and 14.7 psia, and the highest temperature in the cycle is limited to 2500° F to avoid damaging the engine block. Calculate (a) thermal efficiency, (b) net work, and (c) mean effective pressure (d) compare engine efficiency with that of a Carnot cycle engine operating between the same temperatures. 

Mass flow rate, kg/s Mean effective pressure, kPa Polytropic process exponent Pressure, kPa... 

BMEP—brake mean effective pressure, the theoretical average pressure that would have to be imposed on the pistons of a frictionless engine (of the same dimensions and speed) to produce the same power output as uic engine under consideration a measure of how effectively an engine utilizes its piston displacement to do work. 

Capacities.—If n = number of cylinders, S = piston speed, feet per minute, a = piston area, square inches, pm = mean effective pressure, pounds per square inch, the indicated horsepower of a four-cycle single-acting engine is... 

The following values are given for expected mean effective pressures (pm) under good conditions ... 

The duty of a pump is its performance based on the output in foot-pounds per 1,000 lb. of dry steam, or per 100 cu. ft. of air, or per 1,000,000 B.t.u. furnished by the boilers at appropriate pressure. The duty of a steam pump can bo calculated approximately from the indicator diagram (either actual or ideal) by the formula card duty = 144,000 pv, and duty = card duty/E mEs where p = mean effective pressure of whole steam end referred to the area of any one cylinder, v = specific volume of steam at the terminal pressure in this same cylinder, Em — mechanical efficiency, and E = Steam efficiency, comprising all steam losses. 

Mean effective pressure, each steam cylinder.lb. 

Mean Effective Pressure in Multi-stage Compression.—The mean effective pressure, pounds per square inch, with complete intercooling, referred to the l.-p. piston, is expressed by the formula... 

Theoretical horsepower = 0.901Qpi(p2/pi)° — 1 or, for small pressure rise = 0.2618Qpe, where pe = P2 — pi. This formula may also be used for higher pressures if pi = 14.7 lb. per square inch and pe ( = 50.6A) is regarded as the mean effective pressure for adiabatic compression from pi to p2. Table 13 gives values of the mean effective pressure pe against values of p2 — Pi for the usual case of pi = 14.7. 

Centrifugal Compressor Constants and Characteristic Curves—Quantity Constant.—The quantity of gas delivered by a centrifugal compressor is proportional to UaDaha, or, quantity constant = UaDaha- Compressor Constant.— compressor model can be used with practically the same efficiency for various combinations of quantity and pressure such that K = Q/y/p where K is the compressor constant, Q and pe are the desired quantity and mean effective pressure, respectively. The compressor constant can be more conveniently written aaK = QN /pi. ... 

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