JeffT
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- Diesel is diesel is diesel!
Scotty to Captain Kirk"
"Ah, isn't she a beauty, ion propulsion!"
"Ah, isn't she a beauty, ion propulsion!"
Closed Loop Common Rail?
- Thread starter JeffT
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SkyPup
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With the introduction of direct-injection and common-rail technology, the diesel car engine is entering a new phase of credibility. Its combination of performance and economy is now providing a meaningful, all-round challenge to the gasoline engine, particularly in Europe. But Delphi Automotive Systems, which has an extensive research and development facility at its Luxembourg Technical Center, says that despite these advances, one feature of diesel-engine management had been holding back diesel's technical advance: the lack of true, closed-loop control of the injection system. This is significant because an open-loop system cannot accurately compensate for factors such as wear, manufacturing tolerances in the fuel injectors, or for variations in temperature and fuel quality. The company states that gasoline-injection systems have been closed loop for years, and many of the advances in power, refinement, economy, and emissions seen today have been possible because of the real-time feedback that this provides.
Its solution to this problem is an all-new common-rail, direct-injection system that uses an ion sensor to provide real-time combustion data for each cylinder. Developed at its Luxembourg Center, where the majority of Delphi's diesel research and development is conducted, it is said to provide closed-loop control at a cost that will be roughly equivalent to today's best production systems. Dr. Henrich Wied, European Director of Engineering for Delphi Energy & Engine Management Systems, believes that the introduction of a closed-loop system is a major breakthrough. "High-speed, common-rail direct-injection diesel engines are theoretically capable of excellent performance, economy, and emissions, but to achieve this they will require a much higher level of control than is possible with today's technology. With closed-loop systems and ion-sensing technology, we can unlock the potential of diesel engines for automotive applications."
The Delphi ion-sensing system creates an electrical field in the region where combustion starts by introducing a positive dc voltage at the tip of the glow plug. The field attracts the negatively charged particles created during combustion, producing a small current from the sensor to the piston and cylinder walls, which provide a ground. The current is measured by the engine control module (ECM) and processed to provide a signal that is proportional to the applied sensor voltage and to the level of ionization in the vicinity of the sensor. The difference in ionization before and after the start of combustion is quite pronounced, says Wied, allowing the ion-sensing system to provide precise start-of-combustion (SOC) data that can be compared with a table of required SOC timings held by the ECM. The fuel control strategy can therefore be changed from open loop to closed loop, allowing the desired SOC to be maintained for all engine speeds, loads, temperatures, and fuel qualities; and to accommodate production tolerances and wear in each injector. Because the sensing function is combined with the glow plug, no engine modifications are required, and Wied adds that the sensor is in "a near ideal location." One significant feature of the location is that soot build-up, which can reduce the resistance between the sensor and ground, can be easily detected and burnt off through a simple, automated routine.
Delphi regards the precise control of secondary injection events as the most challenging area of diesel engine design for which the new system provides a solution. Wied explains: "To reduce audible noise and NOx, a current production high-pressure common-rail system will typically inject a pilot pulse of around 3-5 mm3 of fuel before the main injection event. Pilot injection can reduce noise by 3-5 dB, but too large a pulse will compromise fuel consumption and emissions. Existing technology can reduce the pilot injection volume to around 1-2 mm3 but only at low injection pressures. Most engine designers would prefer higher pressures because this allows cylinders to be fueled more quickly and for the spray pattern to be improved, leading to increased torque and less smoke."
Delphi's closed-loop system allows a pilot volume of around 0.5-1.0 mm3 under high pressures using standard injectors, and is said to reduce particulates by around 10-20%. The precise volume of the pilot injection can be balanced between cylinders, leading to a further reduction in noise. The adaptively learned injector calibrations can also be applied to post-injection pulses, which provide a more complete combustion and supply HC for active de-NOx catalytic converters. Data from the ion-sensing systems will also be used to meet future OBD requirements.
"With a 0.5-1 mm3 pilot volume at 150 MPa (22 ksi), a 2-3% improvement in fuel consumption can be achieved compared with today's high-pressure systems," explains Wied. "Our system has the capability to eventually run up to 200 MPa (29 ksi), which will increase torque by a further 3-4% as well as provide further emissions benefits."
Pilot production of components for the new system has been established at one of Delphi's European plants, and full production is planned for 2003. Delphi will initially offer a range of compact injectors and is now working on new injector designs to provide real-time rate shaping of the main injection pulse. "Bringing closed-loop control to diesel engines is a very exciting step," says Wied. "With ion sensing, we can provide substantial advances in engine fueling, even without any further developments in engine design or manufacture."
Its solution to this problem is an all-new common-rail, direct-injection system that uses an ion sensor to provide real-time combustion data for each cylinder. Developed at its Luxembourg Center, where the majority of Delphi's diesel research and development is conducted, it is said to provide closed-loop control at a cost that will be roughly equivalent to today's best production systems. Dr. Henrich Wied, European Director of Engineering for Delphi Energy & Engine Management Systems, believes that the introduction of a closed-loop system is a major breakthrough. "High-speed, common-rail direct-injection diesel engines are theoretically capable of excellent performance, economy, and emissions, but to achieve this they will require a much higher level of control than is possible with today's technology. With closed-loop systems and ion-sensing technology, we can unlock the potential of diesel engines for automotive applications."
The Delphi ion-sensing system creates an electrical field in the region where combustion starts by introducing a positive dc voltage at the tip of the glow plug. The field attracts the negatively charged particles created during combustion, producing a small current from the sensor to the piston and cylinder walls, which provide a ground. The current is measured by the engine control module (ECM) and processed to provide a signal that is proportional to the applied sensor voltage and to the level of ionization in the vicinity of the sensor. The difference in ionization before and after the start of combustion is quite pronounced, says Wied, allowing the ion-sensing system to provide precise start-of-combustion (SOC) data that can be compared with a table of required SOC timings held by the ECM. The fuel control strategy can therefore be changed from open loop to closed loop, allowing the desired SOC to be maintained for all engine speeds, loads, temperatures, and fuel qualities; and to accommodate production tolerances and wear in each injector. Because the sensing function is combined with the glow plug, no engine modifications are required, and Wied adds that the sensor is in "a near ideal location." One significant feature of the location is that soot build-up, which can reduce the resistance between the sensor and ground, can be easily detected and burnt off through a simple, automated routine.
Delphi regards the precise control of secondary injection events as the most challenging area of diesel engine design for which the new system provides a solution. Wied explains: "To reduce audible noise and NOx, a current production high-pressure common-rail system will typically inject a pilot pulse of around 3-5 mm3 of fuel before the main injection event. Pilot injection can reduce noise by 3-5 dB, but too large a pulse will compromise fuel consumption and emissions. Existing technology can reduce the pilot injection volume to around 1-2 mm3 but only at low injection pressures. Most engine designers would prefer higher pressures because this allows cylinders to be fueled more quickly and for the spray pattern to be improved, leading to increased torque and less smoke."
Delphi's closed-loop system allows a pilot volume of around 0.5-1.0 mm3 under high pressures using standard injectors, and is said to reduce particulates by around 10-20%. The precise volume of the pilot injection can be balanced between cylinders, leading to a further reduction in noise. The adaptively learned injector calibrations can also be applied to post-injection pulses, which provide a more complete combustion and supply HC for active de-NOx catalytic converters. Data from the ion-sensing systems will also be used to meet future OBD requirements.
"With a 0.5-1 mm3 pilot volume at 150 MPa (22 ksi), a 2-3% improvement in fuel consumption can be achieved compared with today's high-pressure systems," explains Wied. "Our system has the capability to eventually run up to 200 MPa (29 ksi), which will increase torque by a further 3-4% as well as provide further emissions benefits."
Pilot production of components for the new system has been established at one of Delphi's European plants, and full production is planned for 2003. Delphi will initially offer a range of compact injectors and is now working on new injector designs to provide real-time rate shaping of the main injection pulse. "Bringing closed-loop control to diesel engines is a very exciting step," says Wied. "With ion sensing, we can provide substantial advances in engine fueling, even without any further developments in engine design or manufacture."