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The fuel-independent particulate emissions of a direct injection gasoline engine were investigated. This was done by running the engine with reference gasoline at four different loads and then switching to hydrogen or methane port fuel operation and comparing the resulting particulate emissions and their size distribution. Differences in the combustion characteristics of hydrogen and gasoline were accounted for by diluting the inlet air with nitrogen and matching the pressure or heat release traces to those of gasoline operation. Methane operation is expected to generate particulate emissions lower by several orders of magnitude compared to gasoline and hydrogen does not contribute to carbon soot formation because of the lack of carbon atoms in the molecule. Thus, any remaining particulate emissions at hydrogen gas operation must arise from non fuel related sources, e.g. from lubrication oil, metal abrasion or inlet air.

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.

In order to meet future requirements for emission reduction and fuel economy a variety of concepts are available for gasoline engines. In the recent past new pathways have been found using alternative fuels and fuel combinations to establish cost optimized solutions. The presented concept for a SI-engine consists of combined injection of gasoline and hydrogen. A hydrogen enriched gas mixture is being injected additionally to gasoline into the engine manifold. The gas composition represents the output of an onboard gasoline reformer. The simulations and measurements show substantial benefits to improve the combustion process resulting in reduced cold start and warm up emissions and optimized part load operation. The replacement of gasoline by hydrogen-rich gas during engine start leads to zero hydrocarbons in the exhaust gas.

Compressed Natural Gas (CNG) is a promising alternative fuel for internal combustion engines as its combustion is fuel-efficient and lean in carbon dioxide compared to gasoline. The high octane number of methane gives rise to significant increase of the thermodynamic efficiency due to higher possible compression ratios. In order to use this potential, new stratified mixture formation concepts for CNG are investigated by means of numerical fluid simulations. For decades RANS methods have been the industry standard to model three-dimensional flows. Indeed, there are well-known deficiencies of the widely used eddy viscosity turbulence models based on the applied Boussinesq hypothesis. Reynolds stress turbulence models as well as scale resolving simulation approaches can be appealing alternative choices since they offer higher accuracy. However, due to their large computing effort, they are still mostly impractical for the daily use in industrial product development processes.

CNG direct injection is a promising technology to promote the acceptance of natural gas engines. Among the beneficial properties of CNG, like reduced pollutants and CO2 emissions, the direct injection contributes to a higher volumetric efficiency and thus to a better driveability, one of the most limiting drawbacks of today’s CNG vehicles. But such a combustion concept increases the demands on the injection system and mixture formation. Among other things it requires a much higher flow rate at low injection pressure. This can be only provided by an outward-opening nozzle due to its large cross-section. Nevertheless its hollow cone jet with a specific propagation behavior leads to an adverse fuel-air distribution especially at higher loads under scavenging conditions. This paper covers numerical and experimental analysis of CNG direct injection to understand its mixture formation.

The stricter worldwide emission legislation and growing demands for lower fuel consumption and CO2-emission require for significant efforts to improve combustion efficiency while satisfying the emission quality demands. Ethanol fuel combined with boosting on direct injection gasoline engines provides a particularly promising and, at the same time, a challenging approach. Brazil is one of the main Ethanol fuel markets with its E24 and E100 fuel availability, which covers a large volume of the national needs. Additionally, worldwide Ethanol availability is becoming more and more important, e.g., in North America and Europe. Considering the future flex-fuel engine market with growing potentials identified on downsized spark ignition engines, it becomes necessary to investigate the synergies and challenges of Ethanol boosted operation. Main topic of the present work focuses on the operation of Ethanol blends up to E100 at high loads up to 30 bar imep.

A previous study by the authors has shown an efficiency benefit of up to Δηi = 10 % for stratified operation of a high pressure natural gas direct injection (DI) spark ignition (SI) engine compared to the homogeneous stoichiometric operation with port fuel injection (PFI). While best efficiencies appeared at extremely lean operation at λ = 3.2, minimum HC emissions were found at λ = 2. The increasing HC emissions and narrow ignition time frames in the extremely lean stratified operation have given the need for a detailed analysis. To further investigate the mixture formation and flame propagation und these conditions, an optically accessible single-cylinder engine was used. The mixture formation and the flame luminosity have been investigated in two perpendicular planes inside the combustion chamber.

To meet future CO₂ emissions limits and satisfy the bounds set by exhaust gas legislation reducing the engine displacement while maintaining the power output ("Downsizing") becomes of more and more importance in the SI engine development process. The total number of cylinders per engine has to be reduced to keep the thermodynamic disadvantages of a small combustion chamber layout as small as possible. Doing so new challenges arise concerning the mechanical design, the design of the combustion system concept as well as strategies maintaining a satisfying transient torque behavior. To address these challenges a turbocharged 2-cylinder SI engine was designed for research purposes by Weber Motor GmbH and Robert Bosch GmbH. The design process was described in detail in last year's paper SAE 2012-01-0832. Since the engine design is very modular it allows for several different engine layouts which can be examined and evaluated.

This paper describes the continued development of the Navistar 7.3 litre V8 CNG engine. The project background, objectives and preliminary results have already been described (1). Development results show that U.S. 1994 emissions standards can be comfortably met without the use of electronic air fuel ratio control or an oxidation catalyst. Transient cycle emissions of 1.7 g/bhph NOx + NMHC have been obtained from de-rated engines to be used in field demonstration vehicles. Electronic control will allow 2.5 g/bhph NOx + NMHC to be achieved without de-rating. Further emissions reduction without aftertreatment will depend on aftercooling, which also offers the potential for an increased rating.

Ricardo have successfully applied their lean burn gasoline engine technology to spark ignited natural gas engines for industrial applications. An open chamber combustion system using the patented ‘Nebula’ chamber, designed as a simple conversion of a swirling direct injection diesel engine, has been tested as a part of the Ricardo internally funded research programme with very promising results. The tests with a 170 × 170 mm single cylinder research engine have shown that the Nebula gas engine provides fast combustion without excessive cyclic variation up to an air:fuel ratio of 26.5:1 or 1.67 excess air ratio. The test results achieved confirm the potential of the Ricardo Nebula combustion chamber as a lean burn combustion system. Many existing emissions standards were met with good fuel consumption, and the stringent West German and Swiss NOx limits were met at 1200 rev/min without penalties in thermal efficiency through excessive ignition retard.

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.

With current technology, a PEM fuel cell powered vehicle requires a plentiful supply of clean hydrogen to achieve good performance. This can be made available via an on-board methanol reformer. Before the reformer reaches operating temperature it is necessary to obtain energy from an alternative source, such as a battery, in order to power the vehicle. This paper introduces a dynamic model of a methanol reformer fuel cell powered vehicle. The vehicle model is driven over the FTP drive cycle, from a cold start, using various warm up strategies. In this way, different strategies are evaluated in terms of performance and fuel efficiency.

In a study using a single-cylinder engine a significant potential in fuel efficiency and emission reduction was found for stratified operation of a high pressure natural gas direct injection (DI) spark ignition (SI) engine. The control of the mixture formation process appeared to be critical to ensure stable inflammation of the mixture. Therefore, optical investigations of the mixture formation were performed on a geometric equivalent, optically accessible single-cylinder engine to investigate the correlation of mixture formation and inflammability. The two optical measurement techniques infrared (IR) absorption and laser-induced fluorescence (LIF) were employed. Mid-wavelength IR absorption appeared to be qualified for a global visualization of natural gas injection; LIF allows to quantify the equivalence ratio inside a detection level. While LIF measurements require complex equipment, the IR setup consists merely of a black body heater and a mid-wavelength sensitive IR camera.