The effective power of the engine.

Part display power expended on overcoming frictional forces within the engine and its actuation auxiliary units - fan and water pump, the electric ignition devices and other fuel pump; so the power of the engine, which can be used to do useful work effectively and which is called the effective capacity N_э , will always be less than the power indicator:

N_э = N_i – N_Т, (57)

where N_Т , called the power of friction, is himself the power of the indicator, which is used to overcome friction forces and to drive auxiliary units. By analogy with the expression (56), effective power N_э and for power frictions N_Т , given expression;

N_э = p_э , (58)

N_Т = p_Т , (59)

where

p_э kg/sm² - conditional value is called the mean effective pressure;

p_Т kg/sm² - conditional value called the pressure of friction.

Mean effective pressure p_э , is that part of the mean indicated pressure p_i , which can be used for useful work effectively The mean friction pressure is that part of the mean indicated pressure, which is consumed in overcoming the friction in the engine and drive auxiliary.

Mechanical efficiency is the ratio of effective power to the display:

h_м = N_э / N_i , (60)

N_э = h_м N_i , (61)

from the expressions (56), (57) and (61):

p_э = p_i h_м (62)

from the expressions (56), (57), (58) and (59):

p_э = p_i – p_Т (63)

according to the value of the experimental data p_Т for petrol engine equal

p_Т =0,35 + (0,115-0,15)с_т , (64)

for diesel

p_Т =0,9 + (0,11-0,15)с_т (65)

where с_т – average piston speed in m / sec

FIG 15 and 16, given the nature of changes h_м and p_э of the number rater crankshaft engine.

After reaching a peak h_м increasing rater crankshaft decreases as the power N_Т increases depending on the increase in rater crankshaft parabolically decreases power indicator after reaching its maximum due to the deterioration of filling. Mean effective pressure p_э decreases in the low speed region, and also because these turns are too large timing, causing deteriorating h_м . After reaching its peak p_э decreases with increasing revolutions, as the power loss increases due to friction, and reduced h_м due to a decrease in the time process of absorption and increase aerodynamic losses.

Specific fuel consumption.

Specific fuel consumption is called in grams per 1 horsepower per (hp) at one o'clock. There are indicator specific fuel consumption g _i one indicator horsepower per (hp) per hour and the brake specific fuel consumption g _э one effective horsepower per hour.

When the hourly fuel consumption, G _T kg /hour, hour flow rate

G_air = a l₀ G _T

where l₀ – theoretically required amount of air for the combustion of one kilogram of fuel, expressed in kg: l₀ it equals the number of moles L₀ air multiplied by the weight into one mole of air. The weight of one mole of air т _в = 28,95 kg/mole at a pressure of 1 kg / cm² and a temperature of 15⁰ C. The air flow rate in one minute.

G_{air min.} = (a l₀ G _T)/60 ; kg/min.

In one cycle of the actual flow rate is equal to:

G_{air min.} = (a l₀ G _T t)/60*2p ; kg/min.

The ratio of the actual amount of air to the theoretically possible is a filling ratio. All fuel consumption is the unit rate multiplied by the engine power.

G_m = =

where g₁ – indicated specific fuel consumption in grams;

V_л – displacement of engine cylinders.

The effective specific fuel consumption.

g_э = 27000

Specific consumption for diesel engines g_э = 170 – 200 g / hp-hr., for carburetor g_э = 230 – 250 g / hp-hr