## 4 Results  
Figure 6 shows the NOx emissions and the EGH performance during the 1000 rpm test. The first thing that must be mentioned is the fact that the standard aftertreatment system (without the EGH) is not capable to fulfil the EURO VI regulation. EURO VI NOx limit has been calculated from the WHTC limit value multiplied by the conformity factor CF: \(NOx_{limit}^{EURO~{}VI}=0.46\times 1.5=0.69\) g/kWh. As can be seen in Figure 6, NOx emissions are higher than the limit > 0.69 g/kWh. Figure 4: Vehicle being tested on the rolling bench. Figure 5: Transient tests carried out to analyse NOx emissions. The new Euro 7/VII, which will be presented at the end of 2021 and expected to come into force on 2025 [23], will develop stricter CO\({}_{2}\) and NOx limits, as well as new tests and limits for non-CO\({}_{2}\) greenhouse gas emissions [24]. There is no decision yet, but some reports point out that NOx limits will be halved from Euro VI, placing the limit around 0.2 g/kWh [25; 26; 27]. Then, the limit value will be \(NOx_{limit}^{EURO~VII}=0.27\times 1.5=0.41\) g/kWh. Around 40% of FTTP, temperature \(T_{b\_EGH}\) presents a great decline and it produces a significant increase of NOx emissions that is well maintained until 65% of FTTP. The vehicle catalytic system needs to achieve temperature much over these values to start its reaction. This explains also the importance of reaching the urea injection target temperature as soon as possible in order to start catalytic conversion at the standard ATS. Without enough temperature (lower than 225 \({}^{\circ}\)C in this test) and without urea solution injected, NOx values remain high within medium range FTTP. However, the inclusion of the EGH had a very positive impact. It can be noticed a significant NOx reduction, specially at medium FTTP range (40-65%). It is remarkable how NOx values without heater \(NOx_{EGH\_OFF}\) descend drastically after temperature \(T_{b\_EGH}\) exceeds the barrier of 260 \({}^{\circ}\)C, onwards 65% of FTTP. This phenomenon can be explained by the injection of AdBlue that drastically increase the SCR efficiency. Ideally, AdBlue injection starts when SCR inlet temperature exceed 220 \({}^{\circ}\)C. In this case it can be observed that the injection starts at 260 \({}^{\circ}\)C. This difference can be explained by the heat loss in the section from the EGH to the SCR and also by the thermal inertia of the SCR substrate that needs a few seconds to reach the temperature injection threshold. It is important to note that this mismatch is present in all tests. Below 260 \({}^{\circ}\)C, in EGH off mode, the trend of \(T_{b\_EGH}\) is mostly influenced by EGR valve that is controlled by ECU manufacturer parameters. On the other hand, using the heater, \(T_{a\_EGH}\) temperatures were always far higher than the AdBlue injection threshold of 220 \({}^{\circ}\)C (275 \({}^{\circ}\)C minimum) and therefore NOx reduction is improved drastically. Note that during \(NOx_{EGH\_OFF}\), EGH was disabled and consequently temperatures \(T_{a\_EGH}=T_{b\_EGH}\). This achievement is maximized at medium FTTP values as \(NOx_{EGH\_ON}\) data registered is below 0.2 g/kWh. This difference is minimized at 90% FTTP as thermal engine produced more heat and temperature values almost coincide in both cases. Consequently, as time passes and FTTP increases, power consumption decreases. The second cycle was set at 1250 rpm, as shown in Figure 7. Unlike Figure 6, in this case the standard aftertreatment system is capable to fulfil the EURO VI regulation. Notice that NOx emission ranges from 0.1 to 0.3 until 65% FTTP. It is a narrow variation explained by the fact that this engine regime produces a greater impact in temperature increment as  
Figure 6: Results from Test 1 including NOx values, FTTP and gas temperatures at 1000 rpm. \(T_{b\_EGH}\) numbers show. At the end of the test both temperatures present the same values (after 250 s).