The extra absorbed energy of service brakes due to Engine 1 retarding power shortage can be simulated with the model using the following steps: (1) Select several operating points from the Engine 2 vehicle control speed maps; (2) calculate the Engine 2 vehicle control speed at each selected operating point; (3) simulate the Engine 1 downhill driving, with the engine brake fully engaged, with the same gear numbers and road grades as Engine 2, and apply the service brakes as necessary to maintain Engine 1 vehicle speeds the same as Engine 2 control speeds; (4) set up the simulation time (vehicle travel time); and (5) calculate the extra absorbed energy of service brakes due to engine retarding power shortage.
Figure 12 shows the retarding powers of Engine 1 and Engine 2 at the selected operating points.
The multi-factor parametric design charts, constructed using the output data of the vehicle downhill control speed simulations with different engine brake retarding powers, transmission gears, and vehicle weights at sea level or high altitude, can be used to analyze the vehicle downhill drivability or compare the vehicle-level engine brake performance difference between different engine brake configurations or different transmissions to quantify the risk of engine retarding power deficiency at both sea level and high altitude downhill driving conditions.
This analysis approach provides comprehensive interactions among engine brake design, calibration, transmission selection, and operation factors including engine brake (full or partial) retarding power levels, parasitic losses (i.e., engine auxiliaries, vehicle drag, and tire rolling resistance), vehicle weight, downhill road grade, transmission gear selection, vehicle downhill driving speed limit, and maximum engine speed limit.
The impact of the flood retarding structures on streamflow for the wet climatic condition was similar to that described for the average climatic condition.
Figure 7 illustrates the simulated daily streamflow with and without the flood retarding structures for the period from 7/1/92 to 12/31/92.
Duration of daily mean flow curves with and without the flood retarding structures for the average climatic condition is presented in Figure 8.
The findings of this study regarding reductions in baseflow due to the presence of the flood retarding structures are opposite to those reported by Kennon (1966).
As indicated in Figure 8 for the average climatic condition, there is an increase of about 4% in the 2 to 50 percentile portion of the curve with the flood retarding structures in place.
The figure reflects the marked shift in the duration of daily mean flow curve for the highest peak discharges comprising the period of record, and represents a 6% decrease in streamflow due to the reduction in flood peaks by the flood retarding structures.
The turbocharger is typically optimized around the positive power cruise condition which results in a turbine that requires significantly more enthalpy than is available during engine braking as there is no heat input from combustion during retarding. This results in the turbocharger operating in an area of the turbocharger map during engine retarding which generates low levels of boost at low engine speed.
With 2 stroke engine brake engine operation, the mass flow is much higher than standard compression release operation resulting in the compressor operating with increased boost and mass flow at low engine speed compared to a 4 stroke CR brake resulting in a significant increase in engine retarding power at low engine speed (Figure 5).
With the increase in engine retarding power at low engine speeds, there is reduced requirement to downshift in order to achieve the desired retarding performance which reduces fuel usage used to accelerate the engine during the downshift to match the shaft speeds, improves driver comfort due to lower engine operation and reduces the potential for engine overspeed through selection of inappropriate ratio.
Performance simulation was performed using to optimize the valve profiles to maximize the engine retarding power while maintaining the engine in acceptable limits.
The interaction of the valve lifts and the turbo are critical to retarding performance while variation in the valve lifts can result in overload of the valvetrain.