## 3 WLTC-Based Analysis of Study Results
### Energy Performance
The ignition timing, controlled by the engine's ECU according to a predefined algorithm, significantly increases thermal efficiency and reduces the exhaust gas temperature. Bioethanol's higher resistance to knocking [36] allows the ECU to advance the ignition timing based on the signal from the knock sensor (Figure 4a), thereby lowering the exhaust gas temperature. In medium- and high-speed driving modes (II and III), exhaust gas temperatures increase and become similar across all tested fuels (E0, E10, and E70), likely due to a greater amount of exhaust energy being utilised for engine cooling and the cooling intensity being adjusted in response to the engine temperature. As engine loads increase, the exhaust gas temperatures upstream and downstream of the catalytic converter rise, reaching maximum values of approximately 800 \({}^{\circ}\)C and 620 \({}^{\circ}\)C, respectively. During the WLTC driving test, the engine load is periodically increased, reduced, or stopped. In hybrid driving, WLTC stop periods are more frequent and extended than in conventional driving, as at low loads, when the battery is sufficiently charged, some or all of the required power is provided by the electric motors. During engine braking periods, the exhaust gas temperatures upstream and downstream of the catalytic converter drop to around 460 \({}^{\circ}\)C and 350 \({}^{\circ}\)C, respectively, in low-speed mode (I), and to approximately 550 \({}^{\circ}\)C and 440 \({}^{\circ}\)C, respectively, in high-speed modes (III and IV). Figure 3: Various settings during WLTC using different fuels: (**a**) throttle opening and ICE speed; (**b**) ICE coolant temperature and catalytic converter temperature. Two main engine control parameters--excess air ratio and ignition timing--were recorded using data from the engine's ECU. The powertrain system of the test vehicle is designed to maintain an air-fuel mixture close to stoichiometric across a wide range of engine operating conditions. At higher power demands, the throttle opens wider to allow more air intake, while the fuel injectors remain open longer to increase fuel delivery. The composition of the air-fuel mixture is monitored and adjusted by the lambda (\(\lambda\)) control system, which uses a wideband oxygen sensor to measure the O\({}_{2}\) concentration in the exhaust gases. This system adjusts the fuel injection rate to maintain an oxygen concentration of 0.5 to 0.6% in the exhaust gas upstream of the catalytic converter over a broad range of operating conditions. The data from the full WLTC 1800 s test and the extended Mode IV (very high speed, 1450-1800 s) (Figure 4b) demonstrate that the ECU maintained an excess air ratio of \(\lambda\) = 1.0 (stoichiometric mixture) over most of the test range. However, during engine startup, the mixture was slightly richened (\(\lambda\) ranged from 0.85 to 0.95), and at reduced loads, the mixture was leaned (\(\lambda\) reached up to 1.23) before engine braking. The average excess air ratio during the WLTC cycle was calculated as \(\lambda\) = 1.012 for EUR fuel. The excess air ratio for EUR and EUR fuels increased by approximately 0.8% and 1.3%, respectively. This increase in excess air with EUR and EUR is corroborated by a slight rise in the O\({}_{2}\) concentration measured by the exhaust gas analyser. Although the lambda control system aims to maintain a stoichiometric mixture, the increase in O\({}_{2}\) concentration indicates that the air-fuel mixture becomes slightly leaner. The engine ECU controls the ignition timing (\(\Theta\)) and the excess air ratio, with feedback from the knock sensor. Analysing the graphs depicting the variation in ignition timing over the WLTC cycle and at high speeds (Figure 4b), we observe that for all fuels, at startup, the ignition timing is set to \(\Theta\) = 5\({}^{\circ}\) before the top dead centre (BTDC). As the vehicle speed increases to its maximum during the WLTC cycle, the engine speed rises to 3000-4000 rpm (Figure 3a), and the load reaches 30-40 kW (Figure 2b).