Exhaust Gas Optimization of Modern Scooters by Velocity Control

TL;DR

The paper tackles inefficient restriction in Euro 5 50 cc scooters by introducing a velocity-controlled TbWS that throttles air flow while maintaining stoichiometric combustion ($\lambda \approx 1$), thereby avoiding ignition-timing restrictions. The authors develop and test a measurement-enabled VC system, finding a 17% reduction in both fuel use and exhaust mass flow at top speed, substantial CO and HC emission reductions, and a modest CO$_2$ reduction, but observed NO$_x$ increases under certain gradients due to faster, hotter combustion. Through a coast-down based load characterization and high-fidelity sensing (crank, pressure, lambda, gas analysis), they show that VC can compress combustion events and raise mean cylinder pressure with a forward ignition shift of about $20.5^{\circ}$, enabling efficient operation with less fuel. While the approach yields real-world fuel savings and emission improvements, NO$_x$ rises warrant careful catalyst and cycle-level considerations, especially for urban WMTC-type operation. Overall, the velocity-controlled TbWS demonstrates a meaningful path toward eco-friendly restriction in small scooters, supported by a robust measurement and analysis framework.

Abstract

This paper investigates the optimization of the exhaust gas composition by applying a velocity-controlled Throttle-by-Wire-System on modern 50 cc scooters (Euro 5). Nowadays combustion-powered scooters are still inefficiently restricted, resulting in an unreasonably high fuel consumption and unfavorable exhaust emissions. The velocity control prevents restriction by negatively shifting the ignition timing and regulates the throttle valve opening instead. Injection quantity, engine speed, ignition timing, cylinder wall temperature, exhaust gas temperature, oxygen sensor data, crankshaft position and in-cylinder pressure were acquired to measure engine parameters. At the same time, vehicle data on the CAN bus, such as throttle opening angle, the rider's acceleration command and vehicle velocity were recorded. For determination of the exhaust gas composition, five probes were sensing CO, CO2, NOx, O2 and HC in addition to the temperature and mass flow. A Peugeot Kisbee 50 4T (Euro 5) serves as test vehicle. The original and the optimized restriction were subjected to various gradients on a roller dynamometer at top speed. Thus, a statement can be made about all operating points of restriction. The resistance parameters required, were previously determined in a coast down test. When driving on level ground, a difference of 50% in the throttle opening leads to a 17% improvement in fuel economy. By measuring the engine parameters, optimum ignition timing could be proven with increasing internal cylinder pressure. Further, 17% reduction in exhaust gas flow was demonstrated. CO emissions decreased by a factor of 8.4, CO2 by 1.17 and HC by 2.1 while NOx increased by a factor of 3.

Figures (8)

• Figure 1: Ignition timing VeloCtr_JK
• Figure 2: Encoder adaption
• Figure 3: Placement of thermocouples
• Figure 4: Test setup
• Figure 5: CAN bus data