Targeted Efficiency Optimisation for Gasoline Engines

The European Union’s mandatory CO2 standards for new passenger cars in 2009 set a 2015 target of 130 g/km for the fleet average of all manufacturers combined, which was met in 2013, with average EU fleet emissions amounting to 129 g/km. Individual manufacturers are allowed a higher CO2 emission value, depending on the average vehicle weight of their fleet. The heavier the average weight of the cars sold by a manufacturer, the higher the CO2 level allowed. Figure 1 shows that in order to meet the future EU emissions regulations, significant increases in gasoline engine efficiency will have to be realised. Open image in new window FIGURE 1 European CO2 targets and the derived average fuel consumptions resulting from efficiency improvements for the C- and D- vehicle segments for European passenger car markets for the intervals 2015-2021 and 2021-2025 (© FEV) Based on two representative vehicles from the C- and D-segment, which meet the present day CO2 targets, it can be demonstrated that there is a need to improve efficiency for the intervals 2015 to 2021 and 2021 to 2025. The CO2 targets of the two vehicles have been converted to specific fuel consumption targets for each of comparison. The common reduction measures — reduction in vehicle mass, reduction of rolling resistance — and electrification of the powertrain (Micro-HEV, Mild-HEV, HEV) are already considered. — In a C-Segment vehicle, the engine is allowed a maximum average fuel consumption of 256 g/kWh in 2021 and for 2025 it should be 223 g/kWh (Micro-HEV). — In a D-Segment vehicle, the engine is allowed a maximum average fuel consumption of 238 g/kWh in 2021 and for 2025 it should be 213 g/kWh (Micro-HEV). The specification of such an average fuel consumption map is readily comparable across different driving cycles and therefore provides a simple way of evaluating the various technologies in a wide scope. In contradiction, the use of micro-hybridisation to advance electrification of the gasoline engine, allows a slight increase in the maximum allowable average Brake Specific Fuel Consumption (BSFC); but the Micro-HEV must be increasingly used in the new fleet of vehicles [3]. In the analysis presented here, a three-cylinder and a four-cylinder gasoline engine are considered: — 1.0-l three-cylinder turbocharged gasoline engine with direct injection, capable of 200 Nm and 90 kW — 1.6-l four-cylinder turbocharged gasoline engine with direct injection, capable of 250 Nm and 115 kW. Both engines are turbocharged and equipped with direct fuel injection and have intake and exhaust cam phasers. Figure 2 shows the full engine operating range of the 1.0-l- and 1.6-l engines with focus on fuel consumption in the New European Drive Cycle (NEDC) and Worldwide Harmonized Light-Duty Vehicles Test Procedure (WLTP) driving cycles for the C- and D-segment vehicles. Open image in new window FIGURE 2 Engine operating range of the 1.0-l and 1.6-l engines with focus on fuel consumption (marked with red/gray outline) on the NEDC and WLTP driving cycles for the C- and D-segment vehicles (© FEV) Comparing the individual engine maps in Figure 2, it is clear to see that the average fuel consumption would be highly influenced by the different driving cycles and target vehicles. Especially when considering the high load WLTP-H (WLTP with highest vehicle mass) cycle, extended areas of the engine map will also need to be optimised. Technologies with efficacy in broad regions of the engine map will definitively have an advantage. To this effect, the next section will analyse the effectiveness of the individual fuel consumption reduction technologies.