It should be noted that these were stable engine conditions, with a coefficient of variation (COV) of the gross indicated mean effective pressure
(IMEPg) of 1.19 for engine condition 3, and 1.22 for engine condition 4.
The engine operations at different throttle conditions showed a varied range of rich and lean misfiring limits around a reference equivalence ratio that corresponds to the respective maximum indicated mean effective pressure
. The observed range of useful equivalence ratios for stable engine operation is wider at half throttle compared to wide-open throttle.
The variation of brake thermal efficiency with respect to the brake mean effective pressure
under various compression ratios is shown in the Fig.4.
The loss mean effective pressure
lmep is the overhead for friction, pumping, and oil and water pump torque.
: Compression ratio N : Nitrogen content of biodiesel: bar [O.sub.X] : oxygen content of biodiesel BMEP : Brake mean effective pressure
: bar References
This fuel 'power' is normalized for displacement D and engine speed n, to define a 'fuel mean effective pressure
', fumep, the factor 1/2 resulting from four stroke operation.
In addition, indicated horse power, break mean effective pressure
and specific fuel consumption calculated from the experiments.
The engine control software for dynamometer testing, developed by Delphi, balances gross indicated mean effective pressure
([IMEP.sub.g]) for each cylinder based on in-cylinder pressure data.
The FAST model provided a Friction Mean Effective Pressure
value for each key point.
Figure 16 presents the pumping loop of three different lifts for the 3.1 bar and 6.1 bar IMEP loads and Figure 17 presents the pumping mean effective pressure
and gas exchange efficiency for the different maximum valve lifts and loads.
ENMEP - Engine Net Mean Effective Pressure
(Average of all cylinders)
In some applications, other quantities, such as indicated mean effective pressure
(imep) and maximum of heat release rate (HRR)  are considered, possibly in addition to abovementioned quantities.