AIRCRAFT INVESTIGATION
performance calculations for the Mercedes D.II WWI aero engine
Mercedes D.II liquid-cooled 6 -cylinder inline engine 120 [hp](89.5 KW)
German engine rating : 121.7 [PS]
introduction : October 1914 country : Germany importance : ***
applications : Friedrichshafen FF29, Halberstadt D.II, Fokker D.I
normal rating : 120 [hp](89.5 KW) at 1400 [rpm] at 0 [m] above sea level
no reduction, direct drive, valvetrain : SOHC
fuel system : oil system :
weight engine(s) dry : 204.0 [kg] = 2.28 [kg/KW]
bore : 125.0 [mm] stroke : 150.0 [mm]
valve inlet area : 23.8 [cm^2] one inlet and one exhaust valve in cylinder head
gasspeed at inlet valve : 25.2 [m/s]
throttle : 90 /100 open, mixture :13.0 :1
compression ratio: 4.50 :1
calculated stroke volume (Vs) : 11.045 [litre]
compression volume (Vc): 3.156 [litre]
total volume (Vt): 14.200 [litre]
engine height : 91 [cm]
power / stroke volume (litervermogen Nl): 8.1 [kW/litre]
torque : 610 [Nm]
engine weight/volume : 18.5 : [kg/litre]
average piston speed (Cm): 7.0 [m/s]
***************************************************************************
intake pressure at 0 [m] altitude Pi : 0.95 [kg/cm2]
mean engine pressure (M.E.P.) at 0 [m] altitude Pm : 5.53 [kg/cm2]
compression pressure at 0 [m] altitude Pc: 6.21 [kg/cm2]
estimated combustion pressure at 0 [m] Pe : 24.83 [kg/cm2]
exhaust pressure at 0 [m] Pu : 3.73 [kg/cm^2 ]
**************************************************************************
compression-start temperature at 0 [m] Tic: 379 [°K] (106 [°C])
compression-end temperature at 0 [m] Tc: 537 [°K] (264 [°C])
average engine wall temperature at 0 [m] : 476 [K] (202 [°C])
Mercedes D.II on display at the Zagreb museum.Notice the waterjackets covering two cylinders
caloric combustion temperature at 0 [m] Tec: 2151 [°K] (1878 [°C])
polytroph combustion temperature at 0 [m] Tep : 2145 [°K] (1872 [°C])
estimated combustion temperature at 0 [m] Te (T4): 2124 [°K] (1851 [°C])
polytrope expansion-end temperature at 0 [m] Tup: 1218 [°K] (945 [°C])
exhaust stroke end temperature at 0 [m] Tu: 1142 [°K] (869 [°C])
*********************************************************************************
emergency/take off rating at 1593 [rpm] at sea level : 124 [hp]
Thermal efficiency Nth : 0.313 [ ]
Mechanical efficiency Nm : 0.786 [ ]
Thermo-dynamic efficiency Ntd : 0.246 [ ]
design hours : 1279 time between overhaul : 41
fuel consumption optimum mixture at 1400.00 [rpm] at 0 [m]: 34.06 [kg/hr]
specific fuel consumption thermo-dynamic : 244 [gr/epk] = 327 [gr/kwh]
estimated specific fuel consumption (cruise power) at 0 [m] optimum mixture : 340
[gr/kwh]
estimated sfc (cruise power) at 1750 [m] rich mixture : 366 [gr/kwh]
specific fuel consumption at 0 [m] at 1400 [rpm] with mixture :13.0 :1 : 381 [gr/kwh]
estimated specific oil consumption (cruise power) : 23 [gr/kwh]
Literature :
DISCLAIMER Above calculations are based on published data, they must be
regarded as indication not as facts.
Calculated performance and weight may not correspond with actual weights
and performances and are assumptions for which no responsibility can be taken.
Calculations are as accurate as possible, they can be fine-tuned when more data
is available, you are welcome to give suggestions and additional information
so we can improve our program. For copyright on drawings/photographs/
content please mail to below mail address
(c) B van der Zalm 28 June 2020 contact : info.aircraftinvestigation@gmail.com python 3.7.4
notes : according Wikipedia displacement : 9.4 litre, this does not correspond with bore 125mm and stroke 150mm, with this bore and stroke displacement is 11.0 litre.