From DieselNet
http://www.dieselnet.com/news.html
Particulate filters at Frankfurt Motor Show
One of the key technological themes during the recent Frankfurt Motor
Show, attended this year by a record 1 million visitors, was
particulate filters for diesel passenger cars.
The application of diesel particulate filters (DPF) on European
passenger cars has had mostly voluntary character. With today's
advanced diesel engines, only the heaviest car models require DPFs to
meet Euro 4 (2005) emission standards (for instance, eighteen current
TDI vehicle versions from Audi--with power outputs from 61 to 233
hp-- fully comply with Euro 4 standards without the need for
particulate filters). Filters were never necessary to meet Euro 3
(2000) limits.
First introduced by the French PSA Group on the Peugeot 607 (Euro 3),
back in 2000, particulate filters were initially opposed by German
car manufacturers. The change in attitude occurred under the
increasing pressure from environmental organizations and the general
public, who demanded that German cars have ultra-low PM emission
levels matching those in Peugeot automobiles.
As apparent from DPF prototypes showed in Frankfurt by most German
manufacturers (Mercedes, Opel, BMW, and Volkswagen), there are
differences between the German and French approach. From the
technical perspective, most German DPF systems are based on catalyzed
particulate filters in various locations and configurations (with the
exception of some VW models, which utilize fuel additive based
system). The PSA system, on the other hand, relies on a cerium fuel
additive for filter regeneration. The PSA system, now fitted in many
car models with Peugeot engines and sold in over 500,000 units, has
been offered as standard equipment. Most of the German filters will
be offered as options at an extra cost to the car buyer. They will be
available only in Euro 4 models, which are offered in markets with
tax incentives for their early introduction. Thus, the initial sales
volumes may be rather low. This different market approach may be also
related to the differences in filter technology. Fuel additive based
systems can be designed to tolerate the Euro 3 level of sulfur (350
ppm) in the fuel. In contrast, catalyzed filters which utilize high
loadings of active platinum catalyst may produce excessive amount of
sulfate emissions when operated with Euro 3 fuels. Their full
emission benefit may be seen only with the Euro 4 fuel of 50 ppm
sulfur.
Last month we discussed DPF systems from Mercedes, Opel and Vauxhall.
The following is a report on the filter systems from the Volkswagen
group.
+ Audi
Audi AG said it will be launching particulate filters on all Audi
model series with TDI engines. Two prototypes fitted with DPFs were
shown at the Frankfurt Show: A8 3.0 TDI and A4 2.0 TDI. Filters on
Audi models (to be offered as optional extra feature) will utilize
both the catalyzed filter and the fuel additive DPF technologies.
The new Audi A8 3.0 TDI--to be launched in the first half of 2004--
is a luxury saloon car meeting Euro 4 emission standards. The A8 3.0
TDI is powered by a 233 hp, 6-cylinder powerplant, which is the
first production diesel engine to have piezo unit injectors. The A8
3.0 TDI has quattro permanent four-wheel drive and 6-speed tiptronic
as standard.
The particulate filter system for the A8 3.0 TDI is based on a
catalyzed DPF which utilizes a silicon carbide wall-flow monolith
coated with a precious metal catalyst. The filter features a "quasi-
active" (or "passive-active") regeneration, depending on the driving
conditions. The passive regeneration process involves continuous
catalytic oxidation of the particulates deposited in the filter into
CO2. This process takes place within a temperature range of 350 -
500°C which occur predominantly when the car is being driven at
motorway speeds.
If the car is used for a length of time at low loads, such as in
urban traffic, active regeneration support is triggered by the
engine control system. The exhaust gas temperature is actively
raised to around 600°C through a combination of engine management
techniques, including post injection of fuel. In cars with low load
driving patterns, the active filter regeneration occurs every 1,000
to 1,200 km, thus resulting in little fuel economy penalty, said
Audi.
The second DPF-fitted prototype--the A4 2.0 TDI--is powered by a new
two-liter, 4-cylinder diesel engine.
The DPF system on the A4 2.0 TDI utilizes a catalytically active,
iron-based organometallic fuel additive. The additive is added to
the fuel, thus reaching the filter along with the particulates. The
active oxidation of the particulates takes place at temperatures in
excess of 500°C. The additive ash needs to be cleaned from the
filter at intervals of approximately 120,000 km.
http://www.dieselnet.com/news/0309audi.html
+ Volkswagen
VW vehicles exhibited with particulate filters include the new Golf
and Passat. The Passat TDI with 2.0 liters displacement, 136 hp (100
kW) engine will be available with a diesel particulate filter
starting this fall.
This Passat engine is equipped with an additive assisted DPF located
in underfloor position, similar to the Audi A4 2.0 TDI system. The
filter is based on a silicon carbide substrate which utilizes the
composite Si-SiC material. The system uses an iron-based fuel
additive.
VW will successfully introduce particulate filters as standard
equipment on its heaviest models, which will need them to meet Euro
4. Lighter vehicles (from Lupo and Polo to Golf, Bora and Passat)
meet the Euro 4 standards through combustion measures alone. On
these cars, Volkswagen will offer particulate filters as an option.
Volkswagen will also introduce a catalyzed filter located close to
the engine and without additive, which will be offered in 2004.
http://www.dieselnet.com/news/0309vw.html
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