Audi 1.8t ULEV Turbo Gasoline Engine
Audi 1.8t ULEV Turbo Gasoline Engine
Audi 1.8t ULEV Turbo Gasoline Engine
ABSTRACT for the "tier 0" which applied before 1995, to a current
0.07 g/mile (NMOG) for the 2001 model year.
In an age when there is growing tension between To attain these fleet averages, vehicle manufacturers
customer expectations of high engine performance, low are encouraged to offer vehicles with emissions
fuel consumption and compliance with the legal conforming to the stringent limit for Ultra Low Emission
requirements on the emission of airborne pollution, the Vehicles (ULEV) over a distance of 50,000 miles.
ability of a vehicle to meet the most stringent emission
standards is becoming an increasingly important aspect
of its market appeal.
The 1.8 l, 5-valve turbo engine which Audi launched in
1994 represented an emissions concept which, thanks to
its innovative close-coupled catalytic converter, provided
an ideal basis for further development to an engine
meeting the US ULEV emission standard, as the current
engine does [1].
Its configuration as a ULEV concept necessitated the
blanket optimisation of all components which influence
the exhaust emissions. The pistons and injectors were
improved in order to reduce untreated emissions. The
main potential was tapped by incorporating intake
Figure 1: Development of the USA exhaust emission limits
camshaft adjustment and a cascade catalytic converter
for emissions aftertreatment, together with extensive
measures for the engine management system. Since mid-2000, the first vehicle with a turbocharged
The overall concept has enabled Audi to become the gasoline engine that satisfies this ULEV standard has
first car manufacturer to offer an exhaust-gas been available on the US market, in the guise of the
turbocharged gasoline engine that meets the US ULEV Audi A4 1.8 T. Both the manual and automatic versions
emission standard. of this car, whether with front-wheel or quattro drive,
conform to the standard. On the basis of the 1.8 l 5-valve
turbo engine with one main close-coupled catalytic
converter, as first developed in 1994, this engine
1. Introduction impressively extends the downsizing strategy – the
power and torque of a larger engine with fuel
consumption that is in practice close to that of a 1.8 l
Since the mid-1980s, US legislation has required
naturally-aspirated engine – to the field of advanced
vehicles with gasoline engines to meet exhaust emission
emissions technology. The space requirements for
limits. The State of California in particular has specified a
improved emissions control that were inherent to the
gradual reduction in HC and NOx emissions. The
Audi A4's vehicle package and engine design from the
legislation requirements for unburned hydrocarbons
very outset facilitated the implementation of this concept.
specified as the average for all vehicles sold in a given
Growing popularity, with over 300,000 1.8 l turbo
model year have fallen from an initial 0.41 g/mile (THC)
engines built for the VW Group in 1999 and the receipt
of the Top 10 awards "Best Engines of 1997" from the
trade periodical Wards Auto World for the Audi A4 1.8 T 2. Engine-based measures to attain the
and "Best Engines of 1998" for the VW Passat 1.8 T ULEV standard
serve to endorse this concept.
To satisfy the ULEV standard, the engine was further The key challenge in developing a ULEV engine is to
developed on the basis of the LEV engine that has been reduce hydrocarbon emissions, which need to be
available since 1998 and uses the same fundamental virtually halved compared with the LEV standard.
concept. The secondary air system already incorporated Components and the engine management are optimised
into this earlier version, together with engine with the result that exhaust-gas heat brings the catalytic
management with electronic throttle control, were converter to light-off as rapidly as possible.
adopted in modified form. A close-coupled catalytic converter position is essential
At no change to the fuel consumption values, the in order to minimise the heat storage capacities between
maximum power output was raised by 15 kW to 125 kW the engine and the catalytic converter. The heat sink
and the peak torque increased by 15 Nm to 225 Nm created by the interposed turbine is a particular
(between 1950 rpm and 5000 rpm). challenge to the engine developers in the case of this
engine concept.
2.1.1 Pistons
Figure 8: Contribution of individual measures to the ULEV 3.1 Configuration of the catalytic converter
concept
3.1.1. Cold start
0.4
0.3
In a warm operating condition, the catalytic effectiveness The Uniformity Index [5] as a number equivalent to the
is limited only by the transport of mass, assuming quality of the flow distribution amounted to 0,937. The
optimum lambda control in the simulation. This is used portion of the inlet surface area amounts to 91,3 %
influenced primarily by the hydraulic diameter (dh) of the and is therefore quite satisfactory.
channels.
The decisive factors in respect of mechanical durability Sufficiently swift catalytic light-off characteristics in the
are the stability of the catalysts and the bond they form emission test can then no longer be guaranteed. In view
with the mantle and the canning. The high level of of their transient occurrence, these phenomena can
material expansion as a result of the high component scarcely be resolved with conventional temperature-
temperatures, as well as the oscillation of the engine and sensing technology. The use of rapid HC exhaust-gas
the pulsation of the exhaust gas, place extreme sensing techniques in the vehicle, in conjunction with
demands on the catalytic converter in the case of close- highly responsive temperature sensing technology,
coupled concepts. Engines with an exhaust turbocharger made it possible to identify the causes of temperature
are at an advantage thanks to their lower peak-pressure peaks. In this concept, a constant lambda control which
and temperature loads. is capable of establishing specified lambda values
Vibration analyses were carried out for different foil rapidly and accurately means that non-critical exhaust
winding concepts and complete catalytic systems. gas temperatures are assured in all engine operating
A distinction needs to be made between the absolute states.
forces of acceleration and the frequency spectrum in
which the acceleration occurs. The natural resonance A metal support with SM-shaped winding technology,
frequencies of the complete catalytic converter system manufactured by Emitec, has been chosen as the most
must be greater than the highest excitation frequencies suitable catalytic converter support for both the first and
occurring during vehicle operation. the second brick. A comparison of coatings revealed that
The acceleration frequencies were recorded by means coating JM 405 by Johnson Matthey is the best version
of an three-dimensional acceleration transducer up to a in terms of long-term stability and light-off behaviour.
maximum frequency of 6 kHz during full-load engine
start-up from 1000 to 6000 rpm. Figure 13 shows the
acceleration load as a function of frequency. The 4. Results of the exhaust-gas test (FTP-75)
maximum excitation frequency of 4000 Hz is still below
the critical resonance frequency of the selected catalyst
beds and does not lead to any problems. The total In addition to the bag emission results for measurements
acceleration load amounts to 90 g. in the vehicle, exhaust-gas emissions of comprehensive
tests were recorded second-by-second on a dynamic
Amplitude [(m/s2)/Hz] dynamometer were, in order to obtain a better picture of
40 40
the cold-start behaviour in particular. Additional
X-Direction thermocouples were installed ahead of the catalytic
Y-Direction
converter, behind the first monolith and behind the
Z-Direction
30 30 catalytic converter, to determine the temperature of the
gas.
The recorded temperatures show that light-off
20 20 temperature is achieved about 12 seconds after the
engine is started, as intended.
10 10
0 0
0 1000 2000 3000 4000 5000 6000
Frequency [Hz]