# Impact of Exhaust Gas Recirculation on Gaseous Emissions of Turbocharged Spark-Ignition Engines
## 2 Materials and Methods  
For this study, a four-stroke 1.3 L four cylinder, turbocharged, direct-injection spark-ignited engine was used. The main characteristics of the engine are highlighted in Table 1. This engine was also equipped with a variable geometry turbine technology (VGT). Thanks to a variable valve timing system (VVT), intake and exhaust actuations could also be delayed or advanced independently, maintaining the same valve lift and event duration, on a range of 40 crank angle degrees for both the intake and exhaust sides. When the corresponding variables in the engine control unit (ECU) were set to zero, the engine would operate in the minimum overlap condition, whereas values of forty would maximize the valve overlap (i.e., delaying the exhaust and advancing the intake valve profiles). A prototype low-pressure (LP)-EGR line was added to the original engine, extracting the gases after a commercial three-way catalyst. The line consists of an EGR cooler, an EGR valve downstream this cooler, and an intake valve located upstream the compressor, which allows for greater EGR flows when the pressure difference between intake and exhaust lines is low. As generally adopted [15; 26; 31], the EGR rate is calculated from the \(CO_{2}\) concentrations measured at the intake and exhaust lines:  
\[EGR_{rate}=\frac{[CO_{2,int}]-[CO_{2,atm}]}{[CO_{2,exh}]-[CO_{2,atm}]}\times 100 \tag{2}\]  
where \([CO_{2,int}]\) and \([CO_{2,exh}]\) represent the mole fraction of CO\({}_{2}\) at the intake and exhaust, respectively, whereas \([CO_{2,atm}]\) represents ambient mole fraction of CO\({}_{2}\). In particular, the intake CO\({}_{2}\) is sampled in the intake manifold, whereas the exhaust one is measured at the turbine outlet together with the rest of the exhaust emissions. Both are analyzed by means of a HORIBA MEXA-ONE system. The test bench was controlled with AVL-PUMA software, allowing instantaneous speed and engine torque by means of a dynamometric brake AVL AFA 200/4-8 EU. Besides, any modification of the intake and exhaust VVT system, the throttle valve position, and the spark timing were done via a partially opened ECU, which was equipped with an air flow meter to ensure proper lambda control when operating with EGR. The main ECU variables were registered through INCA v7.1. Instead, the VGT and EGR valves were controlled in open loop configuration independently from the ECU based on a National Instruments PXI system, previously described in [32]. The same system was used for high-frequency acquisition. For this purpose, instrumented spark-plugs (AVL ZI33) were mounted in all four cylinders in addition to the instantaneous intake and exhaust manifold pressures (Kistler 4007), measured in their respective manifolds. An AVL optical encoder was installed to provide a crank angle reference for instantaneous pressure measurements with a sampling of 0.2 crank angle degree. The instrumentation was completed with mean pressure and temperature acquisition in the most critical sections of the exhaust, intake, and cooling systems. Other magnitudes such as air and fuel mass flow (AVL FLOWSONIX and 733S, respectively) or the turbocharger speed (MICRO-EPSILON DS05) were also acquired. The engine layout is depicted in Figure 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Magnitude** & **Units** & **Value** \\ \hline Engine type & - & 4-stroke, turbocharged \\ Number of cylinders & - & 4 \\ EGR circuit & - & Cooled low-pressure (LP) \\ Turbocharger & - & VGT \\ Displaced volume & cc & 1300 \\ Stroke & mm & 81.2 \\ Bore & mm & 72 \\ Compression ratio & - & 10.6:1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Engine main characteristics. As stated in the introduction, the main objective of this study is to analyze the impact of different levels of EGR on the exhaust emissions of a turbocharged spark-ignition engine.