## 3 Measurements  
NOx emissions measurements were carried out on a KGHM ZANAM vehicle--more precisely, the LHD LKP-1701 operated in the underground copper ore mine of KGHM Polska Miedz (Poland). This vehicle is depicted in Figure 1, and its general technical specifications are given in Table 1.  
Figure 1: LKP-1701: the LHD vehicle (KGHM ZANAM) [63]. The equipment is specifically designed to operate in the confined spaces of low tunnels and is equipped with a DEUTZ TCD 12.0 V6, which is a turbocharged diesel engine and SCR system, as shown in Figure 2. The relationship between diesel engine power and torque can be found in Figure 3, while a comprehensive list of engine parameters is provided in Table 2. It is important to note that the parameters listed are taken directly from the manuals provided by the diesel engine manufacturer, and the best point consumption refers to diesel fuel with a density of 0.835 kg/dm\({}^{3}\) at 15 \({}^{\circ}\)C.  
Diesel engines are usually operated with an overstoichiometric air-to-fuel ratio to provide the full combustion of soot and to restrict exhausting unburnt fuel. Excess air leads to high NOx emissions. This engine produces 390 kW of power and contains a BlueTec system for exhaust gas after-treatment. This process of NOx emissions reduction is carried out by selective catalytic reduction (SCR) with an ammonia slip catalytic converter and diesel oxidation catalytic converter (DOC). SCR uses Diesel Exhaust Fluid (DEF), or \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Units** \\ \hline Power output as per ISO 14396 & 390 & kW \\ at speed & 2100 & rpm \\ Max. torque & 2130 & Nm \\ at speed & 1400 & rpm \\ Min. idling speed & 600 & rpm \\ Specific fuel consumption & 194 & g/kWh \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The power and torque functions of diesel engine DEUTZ TCD 12.0 V6 [64]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Units** \\ \hline Length & 11,500 & mm \\ Width & 3380 & mm \\ Height & 2350 & mm \\ Gross weight & 48,600 & kg \\ Bucket capacity & 8.6 & m\({}^{3}\) \\ Lifting capacity & 172 & kN \\ Engine power & 390 & kW \\ Driving speed: & & \\
1 st gear & 5.0 & km/h \\
2 nd gear & 9.0 & km/h \\
3 rd gear & 15.0 & km/h \\
4 th gear & 20.0 & km/h \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specification of LKP-1701 [63]. Figure 2: The DEUTZ TCD 12.0 V6 diesel engine with its SCR system [64]. AUS 32 (Aqueous Urea Solution 32%) by ISO 22241. DEF from a special tank is injected into the exhaust pipeline to decompose it to ammonia by the exhaust heat. Inside the SCR catalyst, the ammonia reduces NOx into non-polluting water and nitrogen, which is then released into the atmosphere. The exhaust gas after-treatment unit reads signals from the sensors and transmits them via CAN bus to the engine management control unit: temperature upstream of the SCR catalytic converter; temperature downstream of the SCR; NOx downstream of the SCR; pressure (fluid level) and temperature in the AdBlue/DEF tank; and intake air humidity and temperature. Table 3 presents the standard parameters of the NOx sensor. However, under current regulations, NOx mass measurements must have a minimum accuracy of \(\pm\)20% or \(\pm\)0.1 g/bbp-h [65], which most NOx sensors cannot achieve under transient load conditions. The causes of this include cross-sensitivity to ammonia (NH\({}_{3}\)), exhaust gas flow rate, mass air flow (MAF), or sensor position. Additionally, many sensors have noise levels as low as 10 ppm due to residual amounts of NOx in the exhaust system even when the NOx concentration is zero [66]. Development and validation of a vibration-based virtual sensor are conducted in [67] for real-time monitoring of NOx emissions from a diesel engine. The virtual NOx sensor is validated on a single-cylinder diesel engine bench. The prediction error was less than \(\pm\)10% for the steady-state mode and below \(\pm\)20% for transient conditions.