Honeywell TwoStage Parallel turbo technology was first launched in 2006 as an industry first. Today, it is increasingly in demand among auto manufacturers as they seek to take advantage of the combined benefits of impressive performance, fuel efficiency and emissions control.
TwoStage Parallel turbo systems are typically specified for diesel engines upwards of 2.0L displacement and are ideally suited for V6, V8 and V10 engine configurations.
In a TwoStage Parallel system, two turbos work in sequence. From engine start-up to about 2400 rpm, the primary turbo works on its own – vanes varying from fully-closed position to almost fully-open – while the secondary turbo is inactive. At this stage, the turbine valve and the compressor discharge valve are closed while compressor recirculation valve stays open.
In the phase when engine speeds range from 2400 to 2800rpm, the secondary turbo is activated. At this stage, the turbine valve starts to open while the compressor recirculation valve starts to close, and the compressor discharge valve opens. Vanes close down slightly to enable increased boost during transition and then open up again.
When the engine speed reaches beyond 2800rpm, both turbos are in full sequential mode – vanes opening up to full-open. In this phase, the turbine valve stays open while the compressor recirculation valve is closed, and the compressor discharge valve is open. Honeywell’s patented high-temperature, high-durability turbine control valve, a critical component of the system, is specifically designed to ensure very rapid transition between the two modes of turbo operation.
Honeywell TwoStage Parallel turbo system improves vehicle acceleration by up to 20 percent compared to diesel engines with equivalent displacement. The superior transient behavior enables longer gear ratio strategy. In addition, this turbo system helps reduce vehicle raw emissions while lowering after-treatment complexity and cost – the low thermal inertia enables same catalyst light-off speed as mono-turbo. The system’s superior performance and compact packaging design make it uniquely suited to V-engines.
In the Peugeot 4-cylinder application, the TwoStage Parallel system helped deliver up to 30 percent more torque compared to the company’s 2.2L baseline diesel engine and improve third gear acceleration in the 30-60kph range by 30-50 percent, or a 20 percent reduction in time to speed.
In a recent 3.0L V6 program, Honeywell’s TwoStage Parallel turbo technology helped deliver gains in power and torque of 33 percent and 38 percent respectively (compared with a 2.7L predecessor engine), a 12 percent improvement in fuel consumption and a 10 percent reduction in CO2.
Evolution and Future Trends
Honeywell TwoStage Parallel turbo technology was first introduced in 2006 on the 2.2L 4-cylinder engine on Peugeot 407 and 607, and the Citroen C5 and C6. In 2009, the 3.0L V6 Jaguar XF utilized the aerodynamic advantages of VNT technology for the primary stage, enhancing transient performance through better turbine and compressor efficiency, while an improved turbine valve design enabled raising the temperature capability from 800°C to 830°C, thereby aiding overall emissions performance.
Honeywell’s TwoStage Parallel turbo system is increasingly valued for striking the right balance between performance, fuel efficiency and emissions control. The introduction of latest generation VNT technology, together with options such as ball bearings and new light-weight materials (including TiAl), will further assist auto manufacturers in the development of diesel light vehicles that both excite consumers and comply with ever more stringent environmental standards.