Exhaust Gas Aftertreatment Systems Research Articles

A Phenomenological Approach to Model Diesel Engine Combustion and In-Cylinder Pollutant Emissions Adapted to Control Strategy

Abstract The pollutant emissions becoming more and more constraining, the automotive manufacturers need to adopt a global optimization approach of engine and exhaust after-treatment technologies. Engine control strategies seem to be an essential way to address this issue. The problem is particularly complex, considering the compromise to be reached between the drivability which must be maintained, the reduction of the fuel consumption and the in-cylinder pollutant emissions, and the optimisation of the conditions to reach high conversion efficiencies via exhaust gas after-treatment systems. The development of sophisticated control strategies and models can only be achieved with a complete understanding of the physical phenomena that occur in the combustion chamber, using experimental data and system numerical simulations. In this context, 0D predictive models of combustion and pollutant emissions, calibrated with experimental data, are particularly useful to study a wide range of parametric variations which are difficult and expensive to perform at the testbed. This paper presents an under-development combustion and pollutant emissions model, initially based on the 0D approach of Barba et al. (2000). In order to validate the model on steady state operating conditions, comparisons between experimental measurements and simulations are presented, pointing out the pollutant emissions during variations of loads and engine speeds.

Mechatronic Exhaust Gas Recirculation Valve for Commercial Vehicle Applications

The emission optimization of commercial diesel engines, both on-highway and off-highway, will need further measures to meet the requirements of worldwide strengthening emission laws. In addition to exhaust gas aftertreatment systems also the external exhaust gas recirculation established in passenger cars with diesel engines offers substantial potential for lowering the engine-out emissions of vehicle engines. To this effect, Pierburg GmbH in Neuss, Germany, developed a completely electrically actuated exhaust gas recirculation system for heavy-duty applications.

Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas aftertreatment

The effects of mineral diesel fuel, gas-to-liquid fuel, rapeseed methyl ester, neat soybean and neat rapeseed oil on injection, combustion, efficiency and pollutant emissions have been studied on a compression ignition heavy duty engine operated near full load and equipped with a combined exhaust gas aftertreatment system (oxidation catalyst, particle filter, selective catalytic NO x reduction). In a first step, the engine calibration was kept constant for all fuels which led to differences in engine torque for the different fuels. In a second step, the injection duration was modified so that all fuels led to the same engine torque. In a third step, the engine was recalibrated in order to keep the NO x emissions at an equal level for all fuels (injection pressure, injection timing, EGR rate). The experiments show that the critical NO x emissions were higher (even behind the exhaust gas aftertreatment systems) for oxygenated fuels in case of the engine not being recalibrated for the fuel. GTL and the oxygenated fuels show lower emissions for some pollutants and higher efficiency after recalibration to equal NO x levels.

Development of a Coupling Approach between 0D D.I. Diesel Combustion and Pollutant Models: Application to a Transient Engine Evolution

The constant increase in pollutant emissions constraints has obliged automotive manufacturers to adopt a global optimization approach of engine and exhaust after-treatment technology. Engine control strategies appear to be a powerful solution to address this issue. The problem is particularly complex since acceptable drivability must be maintained whilst at the same time reducing in-cylinder pollutant emissions and ensuring optimum conditions to attain highconversion efficiencies via exhaust gas after-treatment systems. The development of appropriate control strategies can only be achieved with an in-depth understanding of the engine behaviour, using experimental results and system numerical simulations. In this context, predictive combustion and pollutant emissions models, which are calibrated with experimental data, are particularly useful as they allow a wide range of parametric variations to be studied. This paper presents an advanced Diesel combustion model based on a Barba's approach [Barba C. et al. (2000)- A Phenomenological Combustion Model for Heat Release Rate Prediction in High Speed DI Diesel Engines with Common Rail Injection , SAE Technical Paper 2000-01-2933]. This model can be applied to multi-injection, defining a pre-mixed combustion zone for the pilot injection and a diffusion combustion mode for the main injection. To assess the in-cylinder pollutant emissions, a mixing model based on the turbulent kinetic energy generated by the spray, is added to define a burnt gas zone in which post-flame chemistry including CO, NOx and soot formation can be computed. This model is first validated using CHEMKIN and 3D CFD results. Then, using experimental results, a 4 cylinders D.I. Diesel engine is calibrated on steady state engine operating conditions and coupled to an engine control to predict the evolution of pollutant emissions under transient conditions.

Volkswagen’s new 2.0 l TDI engine for the most stringent emission standards — Part 2

Beginning mid-2008, a vehicle will be sold on the US market that complies with the exhaust emission standards Tier 2 Bin5: the VW Jetta. This objective was achieved by applying modifications to the Euro 5 Common-Rail engine already available in Europe for the VW Tiguan and the Audi A4 and by introducing the NOx exhaust gas after treatment system. The previous article provided information on the optimisation of the injection system and on the implementation of low-pressure exhaust gas recirculation and cylinder pressure control. These measures have a decisive impact on the improvement of the raw emissions, on the reduction of the emission range and on the reliability of the engine’s operating procedure. The following article discusses the development of the NOx exhaust gas aftertreatment system and the new operating-mode control for overall system management and also describes the OBD functions.

Volkswagen’s new 2.0 l TDI engine for the most stringent emission standards — Part 1

Having already being launched in Europe in the VW Tiguan and Audi A4, Common Rail engines have been redeveloped to comply with the strictest exhaust fume limits in the world, namely the Tier 2 Bin5 emission legislation in the USA, and will consequently be launched in the VW Jetta there mid-2008. As well as internal engine features like an optimised injection system, a low-pressure exhaust gas recirculation system and a new method of cylinder pressure control, a technical highlight is the implementation of an NOx exhaust gas aftertreatment system. These new engine components require the development of new control algorithms and intensive coordination of parameters for this entirely new combustion process.

KS-1: Development Trends of Heavy Duty Diesel Engines in View of Future European Legislative Requirements(Keynote Papers)

The proposed new European emission standards (EURO VI) to be in force by 2013/2014 are considered very severe, having a NO_x-standard of 0.4 g/kWh in the European Transient Cycle (ETC) together with a low particulate limit of 0.01 g/kWh. Above limits require significant in-cylinder reductions of pollutants as well as exhaust gas aftertreatment for both, nitrogen oxides and particulates. Furthermore, due to the much discussed climate change, the emissions of greenhouse gases (GHG) are to be reduced. For EURO VI, the first step will be to reduce engine-out emissions by means of advanced combustion process development using improved fuel injection equipment, supercharging, exhaust gas recirculation, flexible engine systems, extended engine control and by the mechanical development. Then it would appear that exhaust gas aftertreatment systems are needed. Since approximately 30 % of the fuel input is lost in the exhaust gas, an exhaust gas energy recuperation might be a step forward to reduce fuel consumption and GHG-emissions. In a second part an overview of the EU R&D-project GREEN will be given. In this project, European HD engine manufacturers join forces with suppliers, academia and leading engineering institutes. The common goal is to promote future advanced engine technologies to achieve lower emissions, lower fuel consumption and improved sustainability for future fuels. The main objective of GREEN is to perform research, which will lead to innovative sub-systems for heavy duty engines. The project puts emphasis on diesel engines for trucks and rail applications and on natural gas engines for city transport applications.

Diesel engine development in view of reduced emission standards

Abstract Diesel engine development for use in light-, medium- and heavy-duty road vehicles is mainly driven by more and more stringent emission standards. Apart from air quality related emissions such as nitrogen oxides and particulates, also greenhouse gas (GHG) emissions are likely to become of more and more importance. Furthermore, oil-based fuel availability might become a problem due to limited reserves or due to political influences which leads to significantly increased fuel costs. Based on the above aspects, advanced engine technologies become essential and are discussed. Fuel injection with rate shaping capability and elevated injection pressures, air handling systems to increase the brake mean effective pressures (BMEPs) and specific power with a downsizing approach, while retaining a good dynamic response using possibly two-stage turbocharging. Heterogeneous and near-homogeneous combustion processes where the latter could possibly reduce the requirements on the exhaust gas aftertreatment system. Improvement and further development of engine management and control systems, exhaust gas aftertreatment for a reduction of nitrogen oxides and especially particulates and last but not least, energy recovery from the exhaust gas. Furthermore, alternative fuel usage in road vehicles is becoming important and their application in internal combustion engines is discussed.

Strategies to minimize CO2 and NOx emissions for future gasoline engines

Market trends as well as legislative measures to reduce CO2 emissions significantly require innovative technologies to improve the efficiency of gasoline engines. With this aim, Ricardo’s Lean Boost concept combines direct injection, downsizing by boosting and lean operation under all conditions, however requires a complex exhaust gas aftertreatment system. An alternative approach is Ricardo’s EGR-Boost-technology, featuring charge dilution by recirculated exhaust gas under all operation conditions and thus allowing the use of a conventional three-way-catalyst.

Controlled auto-ignition

Gasoline HCCI, also called Controlled Auto-Ignition (CAI), allows for significant efficiency gains in combination with extremely low NOx emissions when compared to conventional spark-ignited combustion concepts. Bosch’s option to combine a lean-operating direct-injection engine with a simple exhaust gas aftertreatment system (three-way catalytic converter) adds to the attractiveness of CAI.

A Brief Overview on Automotive Exhaust Gas Sensors Based on Electroceramics

Nowadays, ceramic exhaust gas sensors are installed in quantities of millions in automotive exhaust gas systems. Almost any automobile being powered by a gasoline combustion engine is equipped with at least one zirconia exhaust gas oxygen sensor (λ probe) for detection of the air‐to‐fuel ratio λ. The first part of this short overview focuses on potentiometric as well as on amperometric zirconia exhaust gas oxygen sensors. It is remarkable that in the past years a leap in manufacturing technology has occurred from classical ceramic technology to tape and thick‐film technology. The advent of novel combustion concepts like lean‐burn operating gasoline direct injection required novel exhaust gas aftertreatment concepts. It pushed the development of the NOx sensor, which is manufactured in the same technology. It is also shown how development of exhaust gas sensors has always to be considered in interaction with exhaust gas aftertreatment systems. This elucidates why novel sensors have gained in importance just recently when stricter emission regulations were announced, meaning that the time is ripe for novel exhaust gas aftertreatment concepts. Appropriate sensors—ammonia sensors, hydrocarbon sensors, and particulate matter sensors—are still in the R&D stage. Several possible sensor principles are discussed. The materials that are used for sensors in the automotive exhaust are electroceramics. Besides ion‐conducting zirconia and zirconia cermets, electrically insulating alumina is used for substrate purposes. Novel functional materials in the R&D state are strontium–iron titanate for temperature‐independent resistive oxygen sensing and zeolites for selective detection of specific gases like hydrocarbons or ammonia.

Exhaust gas aftertreatment system for Euro 4 heavy-duty engines

“Wall-flow” soot particulate filters for commercial vehicles are not a reliable means of reducing soot particulate emissions, regarding the high kilometrage of more than 1 million, in conjunction with the demand for no maintenance and as little fuel consumption as possible. To fulfil Euro 4 limits the MAN Nutzfahrzeuge Group has developed inner-engine NOx reduction and a PM-Kat system for exhaust-gas aftertreatment. The PM-Kat system with clog-free flow channels permits the reduction of soot particulate emission by continuous oxidation of the separated soot.

AKONDIES — An exhaust concept for a Euro IV passenger car DI diesel engine

The employment of modern diesel engines has drastically reduced particulate emissions from passenger cars over the last ten years. However, reducing both NOx and particulate emissions requires a complex exhaust gas aftertreatment system, especially for heavier vehicles. To this end, Germany’s Federal Ministry of Education and Research sponsored a collaboration project. The objective was to realise an exhaust gas aftertreatment system for a medium-size vehicle with direct injection diesel engine complying with the EURO IV emissions standards planned to come into effect in 2005.

NO2/NO emissions of gasoline passenger cars and light-duty trucks with Euro-2 emission standard

The total amount, as well as the partitioning, of the NOx emissions of six gasoline passenger cars and 10 light-duty trucks, all of Euro-2 emission standard, was measured in this study. The measurements were carried out in the NEDC and FTP75 cycles, in the German “Bundesautobahnzyklus” (federal motorway cycle) and in Swiss real-world cycles. All the vehicles were provided by private owners and brought directly from the road to the chassis dynamometer. In order to obtain results which are as realistic as possible, no servicing was carried out. Depending on their mass, gasoline light-duty trucks of the Euro-2 emission standard have a legal HC+NOx limit which is 20–40% higher than for gasoline passenger cars of the same generation. The measurements show that light-duty trucks emit about eight times more NOx in Swiss real-world cycles compared to passenger cars. However, this cannot be due to the higher engine load alone; there have to be major differences in engine construction, engine tuning or in the layout of the exhaust gas aftertreatment system. It can be observed that the overall catalyst efficiencies of light-duty trucks are substantially lower than those of passenger cars. Apart from this difference in total NOx emissions, an interesting difference in the partitioning of NO and NO2 for passenger cars and light-duty trucks can be observed. On average, about 5.3 mass-percent of the NOx emissions from the measured passenger cars are emitted as NO2, without a clear effect on the velocity pattern driven. In contrast to the behaviour of passenger cars, the measured light-duty trucks show a strong dependence on the velocity pattern. They emit on average 18.4 mass-percent NO2, but this figure goes up to 38.3 percent for motorway driving. The measurements show that the NO2 mass fraction depends strongly on the absolute NOx emission level: the more NOx is emitted, the higher is the NO2 mass fraction.

High-performance ceramic substrates for catalytic converters

Higher performance requirements for exhaust gas aftertreatment systems for passenger cars have led to the development of high cell density substrates with walls thinner than a human hair. Whereas the majority of these substrates have a square cell geometry, the potential for further emission improvements has been predicted for hexagonal cell structures. In order to verify these predictions, Corning has developed a ceramic substrate that combines the features of high cell density, ultra-thin cell walls and hexagonal cell geometry. The emission tests were conducted by Volkswagen, who compared the new substrate concept with square cell ceramic substrates.

Model-based engine control during cold starting of a spark-egnition engine for reduced hydrocarbon emission

Nearly all exhaust gas aftertreatment systems have a finite light-off time. Therefore, engine control is particularly important for emission reduction during cold starting. This article presents a model for the engine control of a spark-ignition engine during cold starting that was developed at the Institute for Internal Combustion Engines at the Technical University of Braunschweig during the FVV project “Cold Start Model”. This model performs a cylinder-specific pre-calculation of the fuel mass that is to be injected for each cycle on the basis of the cylinder pressure.

Particle oxidation catalyst for heavy-duty diesel engines

Most heavy-duty diesel vehicles do not require an exhaust gas after-treatment system as they meet existing Euro-3 emission limits. Euro 4 will reduce particle emissions to one fifth of existing Euro 3 limits and Euro 5 will reduce NOx emissions to 2 g/KWh. A new concept for diesel exhaust after-treatment from Kemira Metalkat Oy is described. The system is a diesel particle oxidation catalyst (POC) using metallic EcoCat substrates. The formation of particulates is described. The development of the POC is outlined. The results of tests to evaluate the catalytic converter showed hydrocarbon and carbon monoxide conversions greater than 80%. Formaldehyde and benzene gave similar conversions.

A study of low-comression-ratio dimethyl ether diesel engines

A new concept of using dimethyl ether (DME) as an alternative fuel in direct injection compression ignition engines with low compression ratios was presented to seek a combustion regime with the highest thermal efficiency. The concept was experimentally evaluated by a comparison of performance and emissions between a DME-fuelled engine and the corresponding conventional diesel engine. The result demonstrated that the DME-fuelled engine is superior to the conventional diesel engine in terms of thermal efficiency, emissions and engine noise, particularly at low compression ratios. However, NOx emission is unacceptably high and needs to be reduced by exhaust gas recirculation (EGR) or after-treatment systems.

HARDWARE IN THE LOOP TESTING OF EOBD STRATEGIES

European regulations regarding exhaust gas emissions have constantly become more restricted in the last decades. Components of the exhaust gas after-treatment system and ECU strategies have become correspondingly more complicated in order to fulfil the prescribed limits. This paper describes how a real time HIL engine simulator can be used to test EOBD ECU strategies, in order to reduce the amount of costly experimental tests. Strategies for the exhaust gas after-treatment system have been tested on HIL. The results of the tests show the feasibility of HIL testing of EOBD strategies.

Computer-aided optimisation of the exhaust gas aftertreatment system of the new BMW 1.8-litre valvetronic engine

The new BMW four-cylinder engine with Valvetronic has a unique market position with respect to performance, comfort, environmental compatibility and fuel efficiency. Within the scope of the development process of the new engine generation, numerical tools have significantly reduced the engineering time and the number of hardware components. This article presents the functional properties of the exhaust gas aftertreatment system and the support of the design process by computational methods.