# Effect of PODE on Emission Characteristics of a China VI Heavy-Duty Diesel Engine
## 2 Experimental Setup  
### Test Engine and Measurement Equipment  
The test engine is a six-cylinder inline Weichai WP12.460 heavy-duty diesel engine in which the inlet air is turbocharged and intercooled. The main specifications of the engine are listed in Table 1. The engine meets China VI emission regulations. The engine is equipped with a common rail fuel injection system.  
The schematic of the experimental setup is presented in Figure 1. The output end of the engine crankshaft is connected to a GW400 eddy current dynamometer produced by Xiangyi Power Test Instrument Co., Ltd. The Horiba MEXA 7100 DEGR gas analyzer is used to measure HC, CO and NOx emissions. Among them, CO is measured by a non-dispersive infrared absorption analyzer (NDIR), HC is measured by hydrogen flame ion analyzer (FID) and NOx is measured by a chemiluminescence analyzer (CLD). The engine exhaust is directly sampled for detection without dilution treatment. In order to reduce the error caused by the fluctuation of the engine operating conditions, the average value of the gas emission concentration of the three measurements is used as the research object. The measurement error and measurement accuracy are shown in Table 2.  
\begin{table}
\begin{tabular}{l l} \hline
**Parameters** & **Values** \\ \hline Number of cylinders & 6 \\ Bore \(\times\) stroke (mm) & \(126\times 155\) \\ Compression ratio & 17 \\ Displacement (L) & 11.596 \\ Rated power (kW) & 340.7 \\ Rated speed (rpm) & 1900 \\ Max torque (N-m) & 2200 \\ Emission regulation & China VI \\ Fuel injection system & CRSN2-16 \\ \hline \end{tabular}
\end{table}
Table 1: Engine specifications.  
Figure 1: The engine test bench, (**a**) the physical map and (**b**) the schematic.  
In the experiments, an AVL 489 Particle Counter is used to measure PN emissions. AVL489 uses n-butanol to wrap a single particulate and detects the number of particles by interfering with the set light path, which can achieve high-precision measurement of the number in the size range of 23 nm\(\sim\)2.5 um emitted by the engine. In order to avoid condensation of volatile hydrocarbon components on the pipe wall, the connecting pipe between the dilution channel and the exhaust pipe is controlled at 150 \({}^{\circ}\)C by electric heating. During the test, in order to avoid data fluctuations caused by changes in the dilution ratio, the total dilution ratio was controlled at 20,000 and remained unchanged.  
In the test, EGR rate can be calculated by Equation (1).  
\[\text{EGR}=\frac{\left(\text{CO}_{2}\right)_{\text{intake}}-\left(\text{CO}_{2} \right)_{\text{ambient}}}{\left(\text{CO}_{2}\right)_{\text{exhaust}}-\left( \text{CO}_{2}\right)_{\text{ambient}}}\times 100\% \tag{1}\]  
where the parameters represent the EGR ratio and the concentration of CO\({}_{2}\) in the ambient, exhaust and intake, respectively. Additionally, the exhaust flow rate can be flexibly adjusted by a throttle valve installed prior to the EGR cooler. As shown in Figure 1, EGR is air-cooled by a plate-fin fan. Additionally, the EGR rate is measured by the HORIBA 7100 DEGR gas analyzer.