As of the beginning of 2017, the number of motor vehicles in our country exceeded 300 million. Motor vehicle emissions are one of the most important sources of atmospheric haze. Therefore, vehicle emissions and energy consumption have always been important research directions for emission reduction and energy saving. In this paper, IOC (intake oxygen concentration) observer and feedforward controller of EGR and VGT are designed based on diesel engine air model. NOx virtual sensor model is designed to detect NOx emission as the feedback variable of IOC observer, and achieve the purpose of accurately measuring the amount of NOx, controlling the EGR valve and the VGT blade in real time, reducing the NOx emission of various diesel engines, improving the fuel economy of the engine and reducing the source of the haze, and there is an important reality in this research and the later promotion and social significance.
Air pollution has become an increasingly serious environmental problem, restricting the rapid development of the political and economic fields in various countries and endangering the normal and healthy life of the people. Although there are many causes of atmospheric pollutants, automobile exhaust is undoubtedly the “repeat offender” [
Therefore, in view of the complexity of the control system mentioned above, this paper designs a control model of EGR and VGT based on the model of diesel air system, and uses the data measured by IOC observer and NOx virtual sensor to largely improve the response speed and stability of the whole control system, and solve the problem of slow response and poor stability of the complex control system so as to reduce NOx emission better.
As shown in
However, EGR may degrade the oxygen concentration in the intake air and cause the engine power to drop. In order to increase the oxygen concentration of the intake air and increase the power of the engine, the VGT needs to be used with EGR. VGT variable cross-section turbocharger system, the exhaust gas was emitted by the engine inertial momentum to promote the turbine chamber turbine, turbine-driven coaxial impeller. Impeller compressed fresh air, through the intercooler, after the pressure into the cylinder by controlling the position of the turning vanes to change the turbine flow area, and then controlling the supercharger speed and supercharging pressure, to ensure the power of the engine, to achieve energy-saving purposes.
air system model and air system settings module as a feedforward controller input. At the same time, the NOx concentration measured by the IOC observer and the NOx emission measured by the NOx virtual sensor are used as the feedback values. The input quantity and the feedback quantity form a closed-loop control system, and finally the lift of the EGR valve and the position of the VGT blade are derived.
Because the physical state annotated in Diesel air system diagram cannot be directly measured. Therefore, we need to establish a model to deduce these physical states that cannot be directly measured, and provide inputs for the following IOC oxygen concentration observer and EGR, VGT feedforward controller research.
As shown in
and pressure. Additionally, the temperature of the intake manifold derives the EGR gas temperature and the EGR gas mass flow rate. Turbine efficiency is derived from turbine mass flow and cylinder gas pressure derived from cylinder gas mass flow and EGR mass flow.
The following are several important models in a diesel air system model:
1) Intake manifold gas quality derivation model.
M ^ int = a 00 + a 10 P int + a 01 W comp N eng + a 20 P int 2 + a 11 P int W comp N eng + a 02 ( W comp N eng ) (1)
2) Intake manifold gas temperature derivation model.
T ^ int = P int V int M ^ int R (2)
3) Cylinder gas mass flow derivation model.
W ^ cyl = V disp 120 V int N eng M ^ int η ^ vol (3)
4) EGR mass flow derivation model.
W ^ egr = 1 T ^ egr ( P ˙ int V int R κ − W comp T ic,ds + W ^ cyl T ^ int ) (4)
5) Exhaust trachea pressure derivation model.
P ^ exh = P turb,ds ⋅ ( d 00 + d 10 W ^ turb T ^ exh P turb,ds + d 01 u vgt + d 20 ( W ^ turb T ^ exh P turb,ds ) 2 + d 11 W ^ turb T ^ exh P turb,ds u vgt + d 02 u vgt ) (5)
6) Turbine gas mass flow.
W ^ turb = W ^ cyl + W fuel − W ^ egr (6)
The observer estimates the oxygen concentration in the exhaust manifold using the air system model and the four known (measured or setpoint) states of the five physical states.
As shown in
So IOC observer control model as formula (7):
[ O ^ ˙ int O ^ ˙ exh ] = A [ O ^ int O ^ exh ] + W + L ( y − y ^ ) = [ a 11 a 12 a 21 a 22 ] [ O ^ int O ^ exh ] + [ w 1 w 2 ] + [ l 1 l 2 ] ( y − y ^ ) (7)
The feedforward controller is designed to precisely control the lift of the EGR valve and the position of the VGT blades to increase the response speed of the control system and thereby reduce NOx emissions.
The parameters in
EGR valve control model as shown in formula (8) below:
u ff,egr = { j 1 ( X egr Y egr j 2 ) 2 + j 3 ( X egr Y egr j 2 ) + j 4 } (8)
Through the compressor power model, the exhaust manifold gas quality model, the turbine power model and the VGT blade model, the control model of the VGT blade position is finally deduced.
VGT blade control model as shown in (9):
u ff,vgr = 1 k 1 [ 1 ( k 2 ⋅ ( X vgt ) + k 3 ⋅ Y vgt − k 4 ] (9)
Compared with traditional sensors, NOx virtual sensors measure the amount of NOx more accurately. At the same time, the measured NOx is used in the control system’s emissions feedback to better respond to the system’s control.
Air System Simulation and Experimental Validation
The image from
For a quantitative analysis of the results, a 5-second average value was obtained using the raw data. The left side of
[g/km] | Horiba | Fast NO | Model |
---|---|---|---|
ECE-15 (NO) | 0.052 | 0.048 | 0.051 |
ECE-15 ((NOx) | 0/075 | x | 0.073 |
EUDC (NO) | 0.211 | 0.206 | 0.195 |
EUDC (NOx) | 0.247 | x | 0.239 |
It can be concluded that the presented model can reliably estimate engine-out NOx. Therefore, this model can be applied to an engine as a good tool forcont rolling engine-out NO and after treatment systems without the need for the NOx sensor. Moreover, the estimation model can be applied to 1-D simulations, such as GT-SUITE and AMESIM, and it shows improved NOx estimation results than that of their own NOx model as the model is able to predict the NO level as same standard as the 3-D CFD simulation.
Li, X.J., Liu, M.O. and Li, C.C. (2018) Research on Diesel Engine Energy Saving and Emission Reduction Based on Air System and NOx Virtual Sensor Model. Open Access Library Journal, 5: e4597. https://doi.org/10.4236/oalib.1104597