SUPERIOR DOWNSIZING
2.3 Production engines with stratified gasoline direct injection (GDI)
2.3.2 Second-generation gasoline direct injection engines
engine displacement: 1984 cm3
Bore ¥ stroke: 82.5 mm ¥ 92.8 mm Valves per cylinder: 4
camshafts: 2
power: 110 kW (150 hp) at 6000 rpm
Maximum torque: 200 nm between 3250 and 4250 rpm emission level: euro 4
cO2 emission: 170 g/km
2.3.2 Second-generation gasoline direct injection engines
Mercedes-Benz and BMW were the first manufacturers to bring second- generation engines with gasoline direct injection, i.e. with spray-guided combustion systems and stratified charging, onto the market in 2006 and 2007.
The M272 de 35 engine has been supplied by Mercedes-Benz in the cLS 350 cGi (charged Gasoline injection) since the end of June 2006 (Lückert et al., 2006). This is a V6 engine with a 3.5 litre displacement volume, four-valve technology with two camshafts per cylinder bank, and piezo injectors with outward-opening nozzles (A-nozzles), positioned centrally in the cylinder head. The spark plug has been slightly displaced from the centre position in the direction of the exhaust valves, and tilted so that the electrodes are positioned at the edge of the injected fuel plume. Fuel is introduced to the combustion chamber using up to three individual fuel injection sequences at a pressure of up to 200 bar. A quantity-controlled three-piston high-pressure pump is used to generate the pressure. Higher stratification rates are possible with spray-guided gasoline direct injection, which means that these engines are potentially more economical to run than engines with first-generation gasoline direct injection.
A double-flow external exhaust gas recirculation system helps reduce NOx
emissions. Two close-coupled three-way catalytic converters ensure that the light-off temperature during cold starts is quickly attained throughout the exhaust gas system, which has a double-flow configuration throughout. The downstream nOx storage converters are mounted on the underbody to protect them against excessively high temperatures. They have an active temperature window of 250–500°c. To enable precise regulation of the nOx catalytic
converters, a temperature sensor is installed upstream of the converter and a nOx sensor is installed downstream of each converter. The latter serves to ensure that the nOx values remain within the limits throughout the entire service life of the vehicle.
in the case of spray-guided systems, it has been possible to considerably extend the engine operating range in which charge stratification takes place when compared to first-generation combustion systems. The CLS 350 CGI can therefore be driven at speeds of more than 120 km/h in stratified charge mode. Two-figure reductions in fuel consumption can be achieved in large sections of the engine operating map. compared to versions with port fuel injection, engines with gasoline direct injection in the new european driving cycle achieve a 10% reduction in fuel consumption. Furthermore, the power output of this engine is 15 kW higher and the torque is 15 nm higher than for the V6 port-injected gasoline engine.
Technical data for Mercedes-Benz CLS 350 CGI
cylinder layout/number: V6
included cylinder-bank angle: 90°
Stroke ¥ bore: 86 mm ¥ 92.9 mm
Stroke–bore ratio 0.926
engine displacement: 3498 cm3
Valves per cylinder: 4
compression ratio: 12.2:1
power: 215 kW (292 hp) at 6400 rpm
Torque: 365 nm at 3000–5100 rpm
Spec. fuel consumption at best point: 240 g/kWh
Fuel consumption at 2000 rpm, 2 bar: 290 g/kWh (port fuel injection:
360 g/kWh)
in 2007, BMW launched new engines with spray-guided gasoline direct injection (Schwarz et al., 2006), starting with the new 3 Series convertible.
A model with an inline six-cylinder engine, twin-turbo charging and high precision injection (hpi) was introduced; it was operated homogeneously.
Additionally, two naturally aspirated versions of the engine with stratified- charge operation were also introduced. These engines all have an identical injection system, the same as the homogeneously operated turbocharged engine. A number of four-cylinder engines with gasoline direct injection and stratified-charge operation are now used as standard by BMW in various vehicle models. These engines are characterised by a centrally positioned injector with a spark plug directly adjacent to it (Fig. 2.11). The injector used is an outward-opening piezo injector with an oil-damped thermal compensator.
This technology has known benefits such as a low coking tendency and an extremely short injector switching time of 200 ms that makes full and partial
strokes, in addition to multiple injection operations, possible. A three-cylinder axial-piston pump with integrated delivery control valve with a combined pressure and delivery control function compresses the fuel up to a maximum pressure of 200 bar. The fuel arrives at the injectors via short separate lines and a common rail with integrated pressure sensor. Specifications for these spray-guided BMW engines can been seen in Table 2.1.
The stratified charge range of an engine with gasoline direct injection and spray-guided combustion system is shown in Fig. 2.12. The fuel consumption of the engine is favourable when operated using a lean mixture throughout a wide load and engine speed range. The best point shows an effective specific consumption of approximately 240 g/kWh.
Fuel consumption is reduced by approximately 13% to 295 g/kWh when compared with an equivalent engine with Valvetronic variable valve timing that already performs extremely favourably. This underscores the potential of gasoline direct injection with spray-guided systems for achieving reductions in fuel consumption and increases in inefficiency.
2.11 Cylinder head BMW (source: BMW).