Lorenzo Pace

An Alternative Way to Reduce Fuel Consumption During Cold Start: The Electrically Heated Catalyst

It is well known that the optimal management of cold start is crucial to fulfill present and future emission legislation. During past years the catalytic converter has left its original under floor position to get increasingly closer to the engine in order to exploit higher exhaust gas temperature. Simultaneously, the exhaust gas temperature is becoming significantly lower, both in gasoline engines due to the extensive use of turbo charging, and in diesel engines thanks to very high combustion efficiency and in some cases the use of two stage turbo charging. A well established way to reach the catalyst light-off temperature fast enough to fulfill emission limits consists of artificially increasing the exhaust gas temperature. This has the drawback of a higher fuel consumption which conflicts with the tight CO2 targets now required of the OEMs. This paper describes an alternative way to warm up the catalytic converter in a fast and efficient manner using the electrical heated catalyst (EHC) with only minor increases of fuel consumption. Additionally, the application of the electrical heated catalyst is very effective in combination with a hybrid vehicle where the EHC itself can be activated via energy recuperation thus increasing the total energy efficiency. INTRODUCTION The origins of the development of the electrically heated catalyst (EHC) go back to the time when the American ULEV legislation was introduced. There was only one way to ensure compliance with the dramatically tightened limit values, especially as far as hydrocarbon (HC) emissions were concerned, and that was through a definite reduction in the light-off phase of the catalyst. One possibility here was to heat the catalyst carrier electrically. A working group between the members of German automotive industry and Emitec was set up and the “EHC” was developed. It consists in a standard metallic substrate with an electrically heated section installed upstream. Initially, it was used for serial production in the Alpina B12 and subsequently in the BMW 750i [1, 2, 3, 4, 7]. In the meantime, however, alternatives such as both engine-based catalyst heating techniques and close coupled catalyst systems were developed, and these were preferred by automotive industry. In recent years, in addition to compliance with the emissions limit values, the achievement of lower CO2 emissions and at the same time lower fuel consumption became a key development area. The subsequent and consistent rise in the efficiency of modern engines, primarily the diesel engine, is leading to a dramatic fall in exhaust gas temperature. This has now reached a level which, depending on the application, load conditions and emissions aftertreatment technology, makes necessary an “external” supply of energy in order to reach a fast light off of the catalytic system to achieve the level of effectiveness required for compliance with the emission limit values [5]. Considering the recent vehicle architecture (availability of electrical energy, energy recuperation etc.), the electrically heated catalyst offers an interesting alternative to purely engine-based catalyst heating strategy. However, it is necessary first of all to consider the question of energy efficiency i.e. how effectively the energy content of the fuel is converted initially into mechanical power and then into heat flux in the catalyst. The evaluation of this efficiency compared with conventional engine heating strategy is the main topic of the next section. THERMAL BEHAVIOUR IN EMISSIONS SYSTEMS As already mentioned in the introduction, the electrically heated catalyst, following a short serial production in spark injection engine applications, became redundant as a result of the introduction of engine-based catalyst heating methods. Therefore, in order to evaluate the energy efficiency of the two systems, an up-to-date spark ignition engine application has been selected. It is well known that the light-off time should be as short as possible in order to comply with emissions requirements, especially with respect to HC. In addition, the light-off temperature of a three-way catalyst (TWC) is usually higher than that of a diesel oxidation catalyst (DOC). This means that for a limited period of time a high level of energy needs to be supplied to the TWC to reach lightoff. Normally no further heating measures are required once the catalytic converter is activated. Fig. 1 shows the temperatures upstream an underfloor catalyst with, and without, engine-based heating strategy and the resulting energy requirement. Fig. 1 : Temperatures upstream of catalyst on SI engine with and without engine-based heating measures. Engine based catalyst heating strategies are usually carried out by artificially deteriorating the combustion process, for example in a gasoline engine using a late ignition point or, in a diesel engine a late injection. Since the resulting combustion is not very efficient then the exhaust gas temperature will be higher. A further strategy possible for DI gasoline engines and diesel engines consists of a particularly late injection in order to have unburned hydrocarbon in the exhaust gas and thus convert fuel energy into heat directly in the catalytic converter via an oxidation process. However, this strategy might increase raw emissions depending on the load point hence it can be only be used to a limited extent. In order to boost the amount of energy supplied to the catalytic converter, the engine speed is also increased with a consequent increased mass flow through the engine and through the catalyst (in some cases it is almost doubled). This gives a significant acceleration in system heating albeit at the price of further fuel consumption increase. Before the energy available in the exhaust gas, as higher mass flow at higher temperature, is transferred to the catalytic converter other parts of the exhaust line upstream of the converter (such as manifold, inlet cone, etc) will partly absorb it . The energy portion absorbed by passive components (i.e. not actively taking part to the catalytic conversion) represents a net energy loss. Conversely, if the catalyst is electrically heated then the required amount of energy can be introduced directly at the catalyst thus avoiding losses to passive components. Moreover, an increase of exhaust mass flow is no longer necessary as the amount of energy needed is clearly reduced. However, in a worst-case scenario the electrical energy needed to heat up the EHC will be obtained from the mechanical energy of the engine dynamics, taking into account the corresponding levels of efficiency. Fig. 2 shows the principal energy flows using engine-based heating techniques as well as electric heating. Fig. 2: Energy flows with engine-based heating and electric heating In order to evaluate the specified losses, a direct-injected turbo-charged gasoline engine fitted with an under-floor catalyst has been examined. ENGINE-BASED CATALYST HEATING Fig. 3 shows the amount of fuel burned in the engine with, and without, catalyst heating (right Y-Axes) and the theoretical obtained energy (left Y-Axes) from the fuel with conversion efficiency of 100%. The efficiency of the catalyst heating strategy is on the other hand given by the ratio between the energy that actually reaches the converter and the theoretical quantity of energy available from the higher fuel consumption. 0 100 200 300 400 500 600 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Time [s] T e m p e ra tu re [ °C ]

Metal Supported Particulate Matter-Cat, A Low Impact and Cost Effective Solution for a 1.3 Euro IV Diesel Engine

Modern Diesel Engines equipped with Common-Rail Direct Injection, EGR and optimized combustion technology have been proven to reduce dramatically engine raw emissions both in terms of Nox and Particulate Matter. As a matter of fact the recently introduced FIAT 1.3 JTD 4 Cylinder Engine achieves Euro 4 limits with aid of conventional 2-way oxidation catalyst. Nevertheless some special applications, such as platforms with relatively higher gross vehicle weight possibly yield to PM-related issues. The present paper deals with the development program carried out to design a cost effective aftertreatment solution in order to address particulate matter tailpipe emissions. The major constraint of this development program was the extremely challenging packaging conditions and the absolute demand to avoid any major impact on the system design. The flow-through metal supported PM Filter Catalyst has been extensively tested on the specific vehicle application with aid of roller bench setup. Partial engine load soot loading, continuous regeneration and long term soot trapping efficiency have been addressed during the present work.

A Computational and Experimental Analysis for Optimization of Cell Shape in High Performance Catalytic Converters

The effects of the internal geometry of catalytic converter channels on flow characteristics; exhaust backpressure and overall conversion efficiency have been investigated by means of both numerical simulations and experimental investigations. The numerical work has been carried out by means of a micro scale numerical tool specifically tailored for flow characteristics within converter channels. The results are discussed with aid of flow distribution patterns within the single cell and backpressure figures along the catalyst channel.

Cold Start Thermal Management with Electrically Heated Catalyst: A Way to Lower Fuel Consumption

Recent engine development has been mainly driven by increased specific volumetric power and especially by fuel consumption minimization. On the other hand the stringent emission limits require a very fast cold start that can be reached only using tailored catalyst heating strategy. This kind of thermal management is widely used by engine manufactures although it leads to increased fuel consumption. This fuel penalty is usually higher for high power output engines that have a very low load during emission certification cycle leading to very low exhaust gas temperature and, consequently, the need of additional energy to increase the exhaust gas temperature is high. An alternative way to reach a fast light off minimizing fuel consumption increase is the use of an Electrical Heated Catalyst (EHC) that uses mechanical energy from the engine to generate the electrical energy to heat up the catalyst. Following this thermal management strategy the energy input can be tailored according to the component need and the energy loss in the system can be minimized. Moreover, the efficiency of such systems can be further optimized using for example brake energy recuperation or advanced thermal management. The present work describes the different engine management strategies tested by Ferrari to find the best compromise between fuel consumption and emission reduction.

Simulationsmodell von Dreiwege- Katalysatoren mit perforierten Folien

Metall-Katalysatoren aus perforierten Folien, wie sie die Emitec GmbH anbietet, ermoglichen im Gegensatz zu Standard-Katalysatoren eine innere Homogenisierung der Stromung. Bei stark inhomogener Anstromung wird damit die Effizienz der Abgaskonvertierung verbessert und der Druckverlust reduziert. Um die Applikation dieser PE-Folienkatalysatoren rechnerisch optimieren zu konnen, wurde bei Arvin-Meritor Emissions Technologies ein neues Simulationsmodell entwickelt, das die physikalischen Vorgange realistisch abbildet.

Backpressure Optimized Metal Supported Close Coupled PE Catalyst - First Application on a Maserati Powertrain

Future stri ge t e issi i its b th i the Eur pea C u ity a d USA require c ti u us y i creased c versi efficie cy f exhaust after treat e t syste s Besides the bvi us targets f fastest ight ff perf r a ce vera c versi efficie cy a d durabi ity cata ytic c verters f r axi u utput e gi es require high y pti i ed f w pr perties as we i rder t create i i u exhaust bac pressure f r w fue c su pti This w r dea s with the desig deve p e t a d seria i tr ducti f a c se c up ed ai cata yst syste usi g the i vative tech gy f Perf rated F i s (PE) By ea s f PE tech gy cha e t cha e gas ixi g withi the eta substrate c u d be achieved eadi g t dra atica y reduced bac pressure va ues c pared with the c ve ti a desig Due t the high y i pr ved f w pr perties f the adva ced eta substrate a c pact c verter c u d be desig ed ta i g i t acc u t the de a di g pac agi g c strai ts i a der V8 e gi e c part e t The prese t paper c sists f u erica si u ati s f w be ch a d e gi e test be ch easure e ts carried ut t assess e issi perf r a ce bac pressure adva tage a d e gi e p wer utput i crease f a c se c up ed si g e bric syste c p ia t with EV II a d EU4 e issi i its

Changing the Substrate Technology to meet Future Emission Limits

Future stringent emission legislation will require high efficient catalytical systems. Along with engine out emission reduction and advanced wash coat solution the substrate technology will play a key role in order to keep system costs as low as possible. The development of metallic substrates over the past few years has shown that turbulent-like substrates increase specific catalytic efficiency. This has made it possible to enhance overall performance for a specific catalytic volume or reduce the volume while keeping catalytic efficiency constant. This paper focuses on the emission efficiency of standard, TS (Transversal Structure) and LS (Longitudinal Structure) metallic substrates. In a first measurement program, standard TS and LS substrates have been compared using a 150cc 4 Stroke engine in dynamic (ECE R40) conditions. In a second test standard and LS substrate have been tested. Both TS and LS technologies show advantage compared to standard technology but have different application fields: TS is a cost effective solution for next emission limits while LS is a possible solution for future stringent emission limits.

Vehicle Mass Lightening by Design of Light-weight Structured Substrates for Catalytic Converters

The clear objective of future powertrain development is strongly characterized by lowest emission impact and minimum overall system cost penalty to the customer. In the past decades emission impact has been primarily related to both optimization of combustion process and exhaust after-treatment system efficiency. Nowadays, weight reduction is one of the main objectives for vehicular applications, considering the related improvements both in fuel consumption (i.e. CO2 production) and engine-out emissions. The state of the art of catalytic converter systems for automotive ZEV-oriented applications has yet to be introduces into mass production. This paper investigates the successful application o metallic turbulent structures for catalytic converters along with innovative packaging considerations, such as structured outer mantle, which lead to significant weight reductions, exhaust backpressure minimization and improved overall emission conversion efficiency. Virtual engineering, such as FEA and CFD simulation, has been used to optimize the substrate (matrix and mantle) and successively a comprehensive test procedure has been carried out to validate the innovative substrate architecture. INTRODUCTION In an effort to minimize the impact of vehicular traffic on the environment and the people living in it, the regulatory authorities are passing more stringent legislation regulating the exhaust gas pollutants. Additionally, increasing attention is drawn to vehicle mass reduction in order to decrease tailpipe CO2 emission. One important approach to achieve this goal is to reduce the exhaust system weight. In particular, the present paper deals on one side with the mass reduction of the catalytic converter addressing both its internal architecture (substrate) and the outer shell (mantle). On the other side, the present work addresses also the optimization of the conversion efficiency both in terms of light-off performance (related to converter’s thermal mass) as well as warm catalyst operation, where mass transfer is the rate limiting step. Since the catalytic reaction only takes place in the walls of the catalyst, the pollutants in the exhaust gas have to diffuse to the wall, where they can undergo reaction. The state-of-the-art ceramic and metal catalysts that are in use today, utilize straight channels that run from one side of the catalyst to the other. Straight channel substrates have good mass transfer at the inlet of the channel, where the flow is still in a turbulent regime. However, the mass transfer rapidly drops as the flow becomes laminar along the channel. In laminar flow the highest concentration of pollutants is at the center of the channel, furthest from the wall. The pollutants have a long diffusion path to access the active reaction sites at the wall. In the present work, innovative substrate technologies are presented that enable both a substrate mass reduction as well as an improvement in conversion efficiency by means of turbulent flow conditions in the single channel.

Turbulent Flow Metal Substrates: A Way to Address Cold Start CO Emissions and to Optimize Catalyst Loading

Modern Diesel Engines equipped with Common-Rail Direct Injection and EGR are characterized by an increasingly high combustion efficiency. Consequently the exhaust gas temperature, especially during a cold start, is significantly reduced compared to typical values measured in previous engine generations. This leads to a potential problem with CO emission limit compliance. The present paper deals with an experimental investigation of turbulent-flow metal substrates, carried out on a vehicle roller bench using a production 1.3 Liter diesel engine equipped passenger car. The tested metal supported catalysts proved to yield extremely high conversion rates both during cold start and in warm operation phase. The improved mass transfer efficiency of the advanced metal substrates is related on one hand to the optimized coating technology and, on the other hand, to the enhanced flow performance in the single converter channels which is caused by structured metal foils. Additionally different cost saving scenarios have been analyzed by means of both catalyst volume reduction and decreased PGM loading.

Simulation model of three-way catalysts with perforated foils

In contrast to standard catalysts, metal catalysts consisting of perforated foils made by Emitec GmbH produce an internal homogenisation of the flow. This improves the efficiency of the exhaust gas conversion and reduces pressure loss especially where the inlet flow is highly inhomogeneous. A new simulation model that realistically reproduces the actual physical processes was developed at ArvinMeritor Emissions Technologies to numerically optimise the application of these PE foil catalysts.