The dynamic emission characteristics are investigated in Sect. 3.6 by a simulation of the dynamic air path model connected to the stationary combustion model. In Fig. 3.13 three typical transients are regarded, which are a step up and down in injection quantity, a ramp up and down in engine speed and a step up and down in injection quantity each followed by a ramp up respectively down in engine speed. The latter two transients can be regarded as acceleration and deceleration event. The same transients, with different set points for the air path states, are investigated by measurements from the engine test bed in Fig. B.3. The engine trajectory is shown in the topmost plot. The air path states are shown in the two plots below and the lower three plots show the combustion outputs.
Figure B.2: Local model outputs of the NOx model showing the 21 local models over the
engine operation points. Model outputs are shown by the black lines and the validity of the local models ˆ.z/ by the grey lines. The shown time window is from the extra urban part of the NEDC.
The predicted combustion outputs are similar to the simulations in Fig. 3.13. The overshoots in NOxemissions are observable for the ramps down in engine speed. These overshoots are due to the
increased air mass per cycle mair, which is however less pronounced for the measured mairsince the
measurement is at the beginning of the intake, see Fig. A.1, which smooths the measured overshoot in air mass per cycle.
The soot peaks are shown by the opacity measurements for the steps up in injection quantity. The dead time of the measurement dynamics is approximately 1 s. The two peaks for the second step up in injection quantity are probably due to a protective mechanism of the Opacimeter because of the high soot emissions. The dynamics in torque measurement are mainly due to the engine speed control of the asynchronous machine. For an engine ramp up, the torque of the asynchronous machine is reduced such that the engine accelerates. This reduced torque is then observable in the
Figure B.3:Measured combustion outputs for a dynamic engine operation. Engine operation
point trajectory is shown in the topmost plot. The first two transients illustrate separately the dynamics in engine speed and injection quantity, whereas the latter can be regarded as typical acceleration respectively deceleration event. The model actuators are adjusted by open loop controls, which is why there are relatively long settling times for mairand p2i(second and third
measurements, see t D 5 6 s and t D 25 26 s. The contrary can be observed for ramps down in engine speed, see t D 10 11s and t D 30 31s.
C
Engine Test Bed
The engine test bed at the Institute of Automatic Control and Mechatronics at the TU Darmstadt is shown in Fig. C.1. It is a high dynamical test bed on which measurements of the engine operation are recorded and new control functions are designed. Control functions can in general be categor- ised into control functions for the test bed automation and control functions for the engine control. The test bed automation mainly includes the control of the engine speed by the asynchronous ma- chine and the control of the engine temperature. The asynchronous machine has a power of 160 kW, a maximum torque of 300 Nm and requires less than 5 ms to adjust a variation in torque. The test engine is mounted on a roller carriage such that various engines can be tested on the test bed. With this roller carriage and the applied plug connections, engines can be changed in a few hours.
Figure C.1:Photos of the test bed at the Institute of Automatic Control and Mechatronics at
the TU Darmstadt. Left picture shows the control room with the test PC, middle picture shows the RCP-Systems and the right picture the test cell with the test engine and the panel to switch between ECU and bypass control of actuators.
The control functions for the test engine can either be realised via the ETK of the ECU or by bypassing the ECU with the RCP-System. The former varies the set points in the ECU and the actuators are still controlled by the ECU, whereas the actuators are directly controlled by the RCP- System for the latter. A manual switch, shown in the upper left of the right picture in Fig. C.1, enables to select between those possibilities. Besides manipulating the actuators, the RCP-system enables to record measurements. Measurements are given for series sensors, which are read from the ECU, and also for additional sensors, which are directly connected to the RCP-system. The lat- ter are recorded either time- or crank angle-synchronous. Crank angle-synchronous measurements are given among others for the in-cylinder pressure sensors with a resolution of 1ıCA. With these
measurements, combustion characteristics, such as the crank angle of 50 % mass fraction burnt 'Q50 are calculated. The real time computation of these characteristics enables the closed loop control of these on the test bed [83]. A schematic overview of the signal flows on the test bed is shown in Fig. C.2.
Figure C.2:Test bed automation at the Institute of Automatic Control and Mechatronics at the
TU Darmstadt. The test PC is the interface to the test bed engineer. Rapid Control Prototyping (RCP) systems are utilised to manipulate the engine control and to record the measurements. The engine control is either manipulated by changes via the ETK of the ECU or by using the bypass and controlling the actuators directly with the RCP-System. Signal flows are indicated as arrows.
The utilised test engine is a Opel/Fiat 1.9 l Common-Rail Diesel engine. It is equipped with a high-pressure egr system and a turbocharger with variable geometry turbine. An additional low- pressure egr system is retrofitted to the engine. A picture of the engine and a data sheet with the main engine characteristics is shown in Fig. C.3. The picture shows various sensor connections and the drive shaft to the asynchronous machine in the lower left. Besides the series sensors, there are additional sensors for temperatures, pressures, actuator positions, the engine torque and the exhaust gas. Exhaust gas measurements are given by a lambda sensor by Bosch, a NOx sensor by NGK,
a Micro Soot sensor by AVL and an Opacimeter by AVL. The soot measurement correlates to the opacity measurement, why these can be used for equivalent investigations of the engine operation. The opacity measurement is therefore applied to validate the model-based smoke limitation, since the Micro Soot sensor is not available for these measurements.
Figure C.3:Left picture shows the test engine with various sensor connections and the drive
shaft to the asynchronous machine at the lower left. The main engine characteristics of the test engine are shown in the table on the right.
D
Mathematical Appendix
D.1
Recursive least squares algorithm
The recursive least squares solution for a linear least squares problem, see eq. (2.8), is given by [67] O w.k C 1/ D Ow.k/ C .k C 1/ y.k C 1/ xT.k C 1/ Ow.k/ (D.1) with .k C 1/ D 1 ˛ C xT.k C 1/P.k/x.k C 1/P.k/x.k C 1/ (D.2) P.k C 1/ D 1 ˛ I .k C 1/x T.k C 1/ P.k/ (D.3)
and the input vector consisting of the grid point weights at the discrete time k
x.k/T D ˆ1.u.k// ˆ2.u.k// : : : ˆL.u.k//
: (D.4)
For an calculation of the recursive least square solution, initial values need to be chosen for the parameter vector w.0/ and the matrix P.0/. If a least squares solution as in eq. (2.8) exists before an adaptation by the recursive algorithm is applied, the initial values can be given as
O
w.0/ D Ow (D.5)
and
P.0/ D XTX 1: (D.6)
If no a-priori information is given, the initial values are chosen as O w.0/ D 0 (D.7) and P.0/ D ˇ 0 B @ 1 0 : :: 0 1 1 C A I ˇ D 100 : : : 10000 (D.8)
With a selection as in eq. (D.8), the influence of the initial value w.0/ vanishes with increasing measurement time. Independent from the initial values, a forgetting factor ˛ 1 has to be chosen. A value ˛ D 1 corresponds to no forgetting and ˛ < 1 enables an adaption to time variant pro- cesses. The corresponding forgetting factor needs then to be chosen with regard to the alteration. A forgetting factor of ˛ > 0:9 is mostly sufficient.