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Tackling Diesel Startup and Emissions With Electronic Control

29 June 2004

beru_psgBeru AG, a leader in diesel cold-start technology, has rolled out a new Instant Startup System (ISS) plus a smart pressure sensor glow plug (PSG) that can play a critical role in minimizing diesel emissions at startup and during all phases of operation. (The image at right is a cross-section of the PSG. Click to enlarge.)

While gasoline engines use a spark plug to ignite the air/fuel mixture, diesel engines rely on the heat of compressed air to ignite a precise amount of fuel to initiate combustion. Heating the air to a minimum starting temperature of 850°C is critical for diesel engine start-up.

In low temperatures, cold intake air and cold cylinder walls hinder attaining the necessary starting temperature. Glow plugs have functioned as an additional heat source at startup to raise the temperature of the intake air to the point necessary to initiate combustion.

Beru’s new Instant Start System can uses optimized glow plugs and an electronic controller that can individually regulate the glow time and voltage for each individual glow plug at any time during operation -- not just at startup.

Operating in conjunction with the control unit of an electronically managed engine, [ISS] aims to ensure optimum combustion conditions during the phases which continue to recur while an engine is operating normally and lead to an increase in the concentration of exhaust pollutants.

Such phases include idling or after extended periods of overrun. At the same time the ISS device targets petrol-style key start, i.e. starting without preheating at temperatures as low 32 degrees F and with only two seconds of glow plug operation at -77 degrees F. Automotive Industries.

The addition of the Pressure Sensor Glow Plug (PSG) to the Startup System provides an even greater deal of intelligent control of combustion. Beru’s goal is to provide control akin to that required in an HCCI engine, with the resulting drop in emissions.

Consequently, research is now focusing on alternative combustion processes such as HCCI (Homogeneous Charge Compression Ignition), which is characterized by its very low NOx emission levels. With this combination, the emission limits would appear to be feasible, and it may even be possible to completely do away with NOx treatment. These new combustion processes require a closed-loop control, with in-cylinder pressure measurement proving to be highly advantageous here. Once the diesel engine has reached a warm running temperature following its cold start, the smart pressure sensor glow plug makes a significant contribution toward reducing emissions, with the aim of making costly exhaust treatment unnecessary as far as possible.

There were some tough engineering challenges to combine these two functions.

BERU equips the glow plug, which is uniquely positioned right in the middle of the combustion chamber in the cylinder to accommodate other microcomponents, with pressure sensor functions. In cooperation with Texas Instruments, BERU integrated a piezo-resistant pressure sensor into the glow plug. In view of the extremely high temperatures, vibrations and pressure ratios in the cylinder head, the mechanical design of the glow plug is a major issue.

The heating element is not incorporated into the body of the glow plug, as is usually the case, but is instead mounted on flexible bearings as a moving part, transmitting the pressure to the membrane. The actual pressure sensor is nowhere near the combustion chamber, and is located in much more favourable conditions. Using a heating element from the BERU Instant Start System, which only glows at the tip, means that the thermal load can be controlled.

The result of the PSG should be reduced noise, fuel consumption and emissions. DaimlerChrysler is using the ISS in its new Mercedes diesels, and according to Beru, at least one major auto manufacturer has already signed up for the PSG. This seems like very good work. I'd love to see corroborating test data.

June 29, 2004 in Diesel | Permalink | Comments (0) | TrackBack (0)

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