Search Results

For a reliable and accurate simulation of SI engines reproduction of their operation limits (misfiring and knock limit) and in this context the knowledge of cyclic combustion variations and their influence on knock simulation are mandatory. For this purpose in this paper a real working-process simulation approach for the ability to predict cycle-to-cycle variations (ccv) of gasoline engines is proposed. An extensive measurement data base of four different test engines applying various operation strategies was provided in order to gain a better understanding of the physical background of the cyclic variations. So the ccv initiated by dilution strategies (internal EGR, lean operation), the ccv at full load and at the knock limit could be investigated in detail. Finally, the model was validated on the basis of three further engines which were not part of the actual development process.

Twenty-three hydrocarbon components were analysed in the exhaust emissions from a 2.3 litre gasoline engine. The effect of a three-way catalyst on emission rates was investigated, as was the effect of addition to fuel of specific aromatic and olefinic compounds. The addition of 1-hexene and 1-octene (olefins) caused statistically significant increases in reactive olefins - ethene and propene - in the exhaust. The addition of benzene and toluene led to increases in these compounds in the exhaust, and indicated that whilst fuel-toluene is the main source of toluene emissions, the emission of benzene has sources in addition to fuel-benzene. A three-way catalyst, when operating at > 600°C, eliminated most hydrocarbons except methane and traces of the light aromatics. At idle, however, the catalyst exhibited substantial selectivity towards different hydrocarbons according to their ease-of-oxidation.

Using an engine simulation code (WAVE) combined with statistical experimental design and optimisation techniques, the potential of a combined Miller cycle and internal EGR heavy duty engine for future truck applications (Euro 3 and 4) has been assessed. The practical issues related to a suitable variable valve timing or actuation system and boosting strategy have been considered. It is found that, whilst internal EGR levels suitable for future European emissions legislation cycles are possible, the boost pressures needed at high load to maintain a suitable air/fuel ratio when running a valve timing strategy to give acceptable levels of in-cylinder temperature (via the Miller system) are beyond the capabilities of current technology. It is believed, however, that such a system may still be suitable for application in markets which have duty cycles less dependent upon full load operation, for example Japan and, possibly, the USA.

To meet LEV and EU Stage III emission requirements, it is necessary for new catalytic converters to be designed which exceed light-off temperature as quickly as possible. The technical solutions are secondary air injection, active heating systems such as the electrically heated catalytic converter, and the close coupled catalytic converter. Engine control functions are extensively used to heat the converter and will to play a significant role in the future. The concept of relocating the converter to a position close to the engine in an existing vehicle involves new conflicts. Examples include the space requirements, the thermal resistance of the catalytic coating and high temperature loads in the engine compartment.

Gaseous emissions were sampled from the exhaust of a single cylinder version of a modern four-valve homogeneous charge spark-ignition engine. The hydrocarbon emissions were extensively analysed using capillary gas chromatography. Levels of key components of the hydrocarbons including methane, benzene and 1, 3-butadiene, were related to fuel composition, mixture strength and exhaust gas recirculation rate. It was shown that the relative levels of hydrocarbon emissions could generally be explained from a knowledge of chemical mechanisms. The significance of the observed trends for the development of engines with reduced levels of hydrocarbon emissions is considered.

Future emissions standards (TIER II, LEV2) require that diesel fuelled vehicles meet the same emissions levels as their gasoline counterparts. In addition, Sport Utility Vehicles (SUVs) must comply to the same norms as passenger cars. However the diesel engine has many desirable attributes for SUV applications and an important role to play in addressing fuel consumption and CO2 emissions issues. In-cylinder reduction of pollutants can no longer be relied upon as the major means to meet future standards. Solutions based solely on emissions control technology are also unlikely to yield positive results. The only viable solution is the combined use of in-cylinder emissions control with advanced catalyst technologies. However, a highly integrated approach is required to gain maximum benefit from the technologies used and enable very low targets to be achieved.

In the quasi-dimensional modeling of the spark-ignition combustion process, the burn rate calculation depends, among other influences, on the laminar flame speed. Commonly used models of laminar flame speeds are usually developed on the basis of measurement data limited to boundary conditions outside of the engine operation range. This limitation is caused by flame instabilities and forces flame speed models to be extrapolated for the application in combustion process simulation. However, for the investigation of, for example, lean burn engine concepts, reliable flame speed values are needed to improve the quality and predictive ability of burn rate models. For this purpose, a reference fuel for gasoline is defined to perform reaction kinetics calculations of laminar flame speeds for a wide range of boundary conditions.

In this paper the development approach and the results of numerical and experimental investigations on homogeneous charge compression ignition in a free piston engine are presented. The Free Piston Linear Generator (FPLG) is a new type of internal combustion engine designed for the application in a hybrid electric vehicle. The highly integrated system consists of a two-stroke combustion unit, a linear generator, and a mass-variable gas spring. These three subsystems are arranged longitudinally in a double piston configuration. The system oscillates linearly between the combustion chamber and the gas spring, while electrical energy is extracted by the centrally arranged linear generator. The mass-variable gas spring is used as intermediate energy storage between the downstroke and upstroke. Due to this arrangement piston stroke and compression ratio are no longer determined by a mechanical system.

In studying H2S emissions, it is desirable to have an analytical technique which is rapid, continuous, accurate and easy to use in a laboratory or vehicle exhaust environment. Typically, H2S has been measured using the EPA impinger method with collection times on the order of 1 to 2 minutes. Other techniques have been developed with significantly shorter response times. However, it has been shown that the major release of H2S occurs in less than 20 seconds after a vehicle changes from rich to lean operation. Therefore, it is highly desirable to have an H2S analytical technique with a response time of less than 10 seconds. In this paper, the benefits of use of a chemical ionization mass spectrometer (CIMS) to continuously monitor H2S and SO2, emissions are reported. Using the CIMS technique, the effects of several operating parameters on the release of H2S and SO2 from automotive catalysts were studied.

Fulfilling exhaust emissions regulations and meet customer performance needs mainly drive the current engine development. Turbocharging system plays a key role for that. Currently turbocharging should provide highest engine power density at high engine speed by also allowing a very responsive performance at low end. This represents a trade-off in turbocharger development. A large scaled turbine allows having moderate exhaust gas back pressure for peak power region, but leading to loss of torque in low engine speed. In the last years of engine development scavenging helped to get away a bit from this trade-off as it increases the turbine mass flow and also reduces cylinder internal residual gas at low engine speed. The mostly in-use lean strategy runs air fuel ratios of closed to stoichiometric mixture in cylinder and global (pre catalyst) of λ = 1.05 to l = 1.3. This will be out of the narrow air fuel ratio band of λ = 1 to ensure NOx conversion in the 3-way-catalyst.

Apart from the reduction of engine-out emissions from the powerplant, the development of an efficient and reliable catalytic converter heating system is an important task of automotive engineering in the future to meet standards that will require reduction of cold start emissions. Carrying out a comprehensive study in this field, BMW has tested and evaluated possible solutions to this challenge. In additon to the electrically heated catalytic converter (E-cat) and the afterburner chamber, an incorporated burner system would meet the requirement for fast catalyst light-off in the future, particularly in the case of larger engines.

A system for stratifying recycled exhaust gas (EGR) to substantially increase dilution tolerance has been applied to a multi-cylinder port injected four-valve gasoline engine. This system, dubbed Combustion Control through Vortex Stratification (CCVS), has shown greatly improved fuel consumption at stoichiometric conditions whilst retaining ULEV compatible engine-out NOx and HC emission levels. A production feasible variable air motion system has also been assessed which enables stratification at part load with no loss of performance or refinement at full load.

The production of the BMW ALPINA B12 5.7 with Switch-Tronic transmission provides the markets of Europe and Japan with an exclusive, luxury-orientated, high performance limited series limousine. This is the first vehicle worldwide to be fitted with the progressive exhaust gas aftertreatment technology known as the Electrically Heated Catalyst (EHC), in which the effectiveness of the power utilized is increased significantly by an alternating heating process for both catalytic converters. Only since this achievement has the implementation of the EHC been viable without extensive modification to the battery and alternator. With this exhaust gas aftertreatment concept, the emissions of this high performance vehicle will fall to less than half the maximum permissible for compliance with 1996 emission standards.

In a joint research project between industrial companies and a number of research institutes, nitrogen oxide conversion in oxygen containing exhaust gas has been investigated according to the following procedure Basic investigations of elementary steps of the chemical reaction Production and prescreening of different catalytic material on laboratory scale Application oriented screening of industrial catalyst material Catalyst testing on a lean bum gasoline engine, passenger car diesel engines (swirl chamber and DI) and on a DI truck engine Although a number of solid body structures show nitrogen oxide reduction by hydrocarbons, only noble metal containing catalysts and transition metal exchanged zeolites gave catalytic efficiencies of industrial relevance. A maximum of 25 % NOx reduction was found in the European driving cycle for passenger cars, about 40 % for truck engines in the respective European test.

The development of future gasoline engines is dominated by the study of new technologies aimed at reducing the engine negative environmental impact and increase its thermal efficiency. One common trend is to develop smaller engines able to operate in stoichiometric conditions across the whole engine map for better efficiency, lower fuel consumption, and optimal conversion rate of the three-way catalyst (TWC). Water injection is one promising technique, as it significantly reduces the engine knock tendency and avoids fuel enrichment for exhaust temperature mitigation at high power operation. With the focus on reducing the carbon footprint of the automotive sector, another vital topic of research is the investigation of new alternative CO2-neutral fuels or so-called eFuels. Several studies have already shown how these new synthetic fuels can be produced by exploiting renewable energy sources and can significantly reduce engine emissions.

It has been shown by calculation that, for given engine operating conditions, there should be an optimum rate of combustion for minimum Nox emissions from spark ignited engines. This paper gives experimental results from a single cylinder engine which confirm the theory, and show that, for a particular engine, the normal combustion rate needed reducing at zero EGR and increasing at high EGR rates, in opposition to its natural tendency to decrease. The effect on economy was a small loss at zero EGR, but an appreciable improvement at high EGR. Cyclic variation and octane requirement studies are also included.

The advantages of closed, loop over open loop control systems are generally recognised. However, existing engine management systems implement most control functions in open loop because suitable feedback sensors are not available. Even for so-called closed loop air fuel ratio controllers, shortcomings of the exhaust gas oxygen (EGO) sensor limit the potential effectiveness of closed loop control. A more direct measure of the combustion process, such as cylinder pressure, can yield sufficient information for the closed loop operation of many of the combustion control functions; this paper presents the results of a prediction algorithm which can derive a variety of feedback signals from cylinder pressure. Cylinder pressure, together with several combustion variables, including air-fuel ratio, exhaust gas recirculation rate, and NOx HC, CO and CO2 emissions were measured at various operating points.

Natural gas is one of the alternative fuels to diesel being considered for low emissions heavy-duty applications. The favoured operating strategies for low emissions SI gas engines are identified as those with high levels of dilution - stoichiometric operation with EGR, and lean-burn. A well-matched exhaust catalyst is needed to produce the lowest emissions levels. Increasing the accuracy of transient air-fuel ratio control is shown to improve the emissions still further. The most favourable combinations of engine operating strategy and control accuracy are identified with respect to fuel economy and first cost. The Co-Nordic Natural Gas Bus Project is an example of an engine development programme aimed at achieving the lowest possible exhaust emissions levels, and as such uses the lowest emissions approach of a stoichiometric engine strategy with EGR and high accuracy control.

For the BMW V8 engine, a new LEV/EU3 emission concept has been developed by improvements to the previous engine management and secondary air supply and a complete new exhaust system. Beside the emission limits, also high engine output targets and high operating reliability were targeted. In addition the new exhaust system had to meet low cost targets. Based on these requirements an exhaust concept with separate pre catalyst and main catalyst was chosen. To reduce the heat mass and to optimize the pressure drop, 4.3mil/400cpsi thin wall ceramic substrates were used for the pre and main catalyst.

It is expected that heavy duty engine legislation in Europe will continue to drive down test cycle BSNox emissions to levels of between 2.5 and 3.5 g/kWh by 2005, with a reduction in particulate emissions to between 0.02 and 0.08 g/kWh. It is unlikely that re-optimisation of existing engine combustion systems alone, such as further retardation of the fuel injection timing, will be sufficient to meet the legislated BSNox targets. Other measures, such as cooled EGR or new aftertreatment systems must therefore be considered. Such emissions control strategies may conflict with other market requirements for improved fuel consumption and increased power density. In this paper, research at Ricardo into the configuration of a premium heavy duty truck engine for the European market for model year 2005 and beyond, is described. A review of the market requirements, projected to 2005 was undertaken in order to define the specification of the concept engine.