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Engines with gasoline direct injection promise an increase in efficiency mainly due to the overall lean mixture and reduced pumping losses at part load. But the near stoichiometric combustion of the stratified mixture with high combustion temperature leads to high NOx emissions. The need for expensive lean NOx catalysts in combination with complex operation strategies may reduce the advantages in efficiency significantly. The Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. The mainly homogeneous lean mixture leads to low combustion temperatures and subsequently to low NOx emissions. By additional EGR a further reduction of the combustion temperature is achievable. The BPI concept is realized by a prechamber spark plug and a piston bowl. The main feature of the concept is its dual injection strategy.

For spark ignition engines, the most effective way to reduce the overall fuel consumption and CO2 emissions respectively is the implementation of gasoline direct injection technology. In comparison to the current wall and air guided systems, the direct injection system of the second generation - the spray guided DI- is the most promising one with respect to fuel economy and emission. In order to exploit its full potential, a thorough combustion process development regarding injector and spark plug design and their positioning within the combustion chamber is essential. Especially multihole injectors offer many degrees of freedom with regard to the nozzle shape and spray pattern. To reduce the development work and costs necessary to identify the ideal nozzle characteristic and spray pattern, reliable CFD models are necessary.

When developing effective exhaust emission reduction measures, a better understanding of the complex working cycle in crankcase scavenged two-stroke gasoline engines. However, in a two-stroke gasoline engine detailed measurement and analysis of combustion data requires significantly more effort, when compared to a lower speed four-stroke engine. Particularly demanding are the requirements regarding the high speed (>10,000 rpm) which inevitably goes along with heavy vibrations and high temperatures of the air cooled cylinders. Another major challenge to the measuring equipment is the increased cleaning demand of the optical sensor surface due to the two-stroke gasoline mixture. In addition, the measuring equipment has to be adapted to the small size engines. Therefore, only a fiber optical approach can deliver insight into the cylinder for analyzing the combustion performance.

A multi-optical fiber measurement technique is presented which can determine spatial flame propagation with a high temporal resolution. With this measurement technique it is possible to investigate the combustion process in both Diesel and SI engines. The measurement technique can also be applied for the detection of flame propagation in research engines and in actual production engines for performing analysis of special problems such as knocking combustion, combustion chamber design studies which concern flame propagation, the influence of engine parameters on flame propagation, ignition and inflammability behavior. The new measurement technique is discussed in detail and the application of optical measuring points in the combustion chamber walls is demonstrated. A special non-contacting optical transmission system has been developed for the observation of flame propagation.

We have performed simulations and experiments to characterize the mixture formation in spray-guided direct injected spark ignition (DISI) gasoline engines and to help to understand features of the combustion process, which are characteristic for this engine concept. The 3-D computations are based on the KIVA 3 code, in which basic submodels of spray processes have been systematically modified at ETH during the last years. In this study, the break-up model for the hollow-cone spray typical for DISI engines has been validated through an extended comparison with both shadowgraphs and Mie-scattering results in a high-pressure-high-temperature, constant volume combustion cell at ambient conditions relevant for DISI operation, with and without significant droplet evaporation. Computational results in a single-cylinder research engine have been then obtained at a given engine speed for varying load (fuel mass per stroke), swirl and fuel injection pressure.

The physical behavior of the combustion process in a jet-guided direct injection spark ignition engine has been investigated with three different measurement techniques. These are flame visualization by use of endoscopy, ion-current sensing at 16 different locations in the combustion chamber and the estimation of the flame temperature as well as soot concentration based on multi-wavelength-pyrometry. The results of all these measurement techniques are in good agreement between each other and give a coherent picture of the physical behavior of the combustion process and make it possible to characterize the main influence parameters on combustion. This serves as a basis for validation and improvement of simulation tools for the engine thermodynamics and combustion.

Optical measurement technique became more and more common for the last few years. Especially optical fibre technique is often used to detect flame propagation. With optical sensors the ignition process can be investigated with high temporal and spatial resolution. An in-cylinder optical sensor has been developed and tested to analyze the ignition of mixture and luminous emission of burning gas. The sensor consists of eight optical probes fitted in a conventional spark plug. The results show good correlation between measured luminosity and combustion parameters such as load, engine speed, ignition timing and air-fuel mixture ratio. A correlation between development of light intensity and pressure was found. For evaluation of light signals different analysis methods are presented. Furthermore it is shown that the luminosity of the flame can be used to control the combustion process.

The emission behaviour of an internal combustion engine under test-bed conditions shows differences to the emission behaviour under real in-use conditions. Because of this fact, the developers of combustion engines and the legislator are focussing on the measurement and optimization of real in-use emissions. To this day, the research, the adjustment of the carburettor and the legislation of small handheld engines is performed under test bench conditions, especially conditioned fuel pressure and temperature, as well as air temperature. Also the engines are laid out for two operation points: rated speed with full open throttle and idle speed. This test-procedure is used for all kinds of handheld off-road applications and does not consider the load profile of the different power tools. Especially applications with transient load profiles, for example chainsaws, work in more than two operating points in real use.

The continuous pursuit of more efficient diesel engines and the stricter emission regulations with the introduction of the Real Driving Emissions test (RDE) necessitate further investigations of heating strategies and their suitability in terms of series production. Under these circumstances heating strategies of a variable valve train for a single-cylinder research diesel engine have been first simulated and then experimentally tested at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology (KIT). By combining statistical experimental design (DoE) and 1-D gas exchange simulations, empirical DoE models for the design of suitable camshaft configurations have been established. After having performed a potential assessment, the most favorable configurations were manufactured and subsequently tested.

Rapeseed oil can be a possible substitute for fossil fuel in Diesel engines. Due to different physical properties of rapeseed oil like higher viscosity and higher compressibility compared to diesel fuel, rapeseed oil cannot be easily used in conventional Diesel engines without modifications. Especially incomplete combustion leads to deposits in the combustion chamber and higher exhaust gas emissions. These unfavorable characteristics are caused primarily by insufficient mixture preparation. The adjustment of the injection system will improve the mixture preparation and the combustion of a Diesel engine, operated with rapeseed oil. The nozzle geometry is the main parameter of the whole injection system chain to realize a better combustion process and so higher efficiency and lower exhaust gas emissions.

Advanced thermal management systems in passenger cars present a possibility to increase efficiency of current and future vehicles. However, a vehicle integrated thermal management of the combustion engine is essential to optimize the overall thermal system. This paper shows results of an experimental heat flux analysis of a state-of-the-art automotive diesel engine with common rail injection, map-controlled thermostat and split cooling system. Measurements on a climatic chamber engine test bench were performed to investigate heat fluxes and energy balance in steady-state operation and during engine warm-up from different engine start temperatures. The analysis includes the influence of the operating point and operating parameters like EGR rate, injection strategy and coolant temperature on the engine energy balance.

In the present paper the results of a set of experimental investigations on LSPI are discussed. The ignition system of a test engine was modified to enable random spark advance in one of the four cylinders. LSPI sequences were successfully triggered and exhibited similar characteristics compared to regularly occurring pre-ignition. Optical investigations applying a high speed camera system enabling a visualization of the combustion process were performed. In a second engine the influence of the physical properties of the considered lubricant on the LSPI frequency was analyzed. In addition different piston ring assemblies have been tested. Moreover an online acquisition of the unburned hydrocarbon emissions in the exhaust gas was performed. The combination of these experimental techniques in the present study provided further insights on the development of LSPI sequences.

As an important means of engine development and optimization, modelbuilding plays an increasingly important role in reducing carbon dioxide emissions of the internal combustion engines (ICEs). However, due to the non-linearity and high dimension of the engine system, a large amount of data is required to obtain high model accuracy. Therefore, a modelling approach combining the experimental data and prior knowledge was proposed in this study. With this method, an artificial neural network (ANN) model simulating the engine brake specific fuel consumption (BSFC) was established. With mean square error (MSE) and Kullback-Leibler divergence (KLD) serving as the fitness functions, the 86 experimental samples and constructed physical models were used to optimize the ANN weights through genetic algorithms.

The concept of hot surface assisted compression ignition (HSACI) was previously shown to allow for control of combustion timing and to enable combustion beyond the limits of pure homogeneous charge compression ignition (HCCI) combustion. This work investigates the potential of HSACI to extend the operating limits of a naturally aspirated single-cylinder natural gas fueled HCCI engine. A zero-dimensional (0D) thermo-kinetic modeling framework was set up and coupled with the chemical reaction mechanism AramcoMech 1.3. The results of the 0D study show that reasonable ignition timings in the range 0-12°CA after top dead center (TDC) in HCCI can be expressed by constant volume ignition delays at TDC conditions of 9-15°CA. Simulations featuring the two-stage combustion in HSACI point out the capability of the initial heat release as a means to shorten bulk-gas ignition delay.

Particulates and nitrogen oxides comprise the main emission components of the Diesel combustion and therefore are subject to exhaust emission legislation in respective applications. Yet, with ever more stringent emission standards and test-procedures, such as in passenger vehicle applications, resulting exhaust gas after-treatment systems are quite complex and costly. Hence, new technologies for emission control have to be explored. The application of non-thermal plasma (NTP) as a means to perform exhaust gas after-treatment is one such promising technology. In several publications dealing with NTP exhaust gas after-treatment the plasma state was generated via dielectric barrier discharges. Another way to generate a NTP is by a corona high-frequency discharge. Hence, in contrast to earlier publications, the experiments in this publication were conducted on an operated series-production Diesel engine with an industrial pilottype corona ignition system.

Particle number measurements during different real world and legislative driving cycles show that catalyst heating, cold and transient engine operation cause increased particle number emissions. In this context the quality of mixture formation as a result of injector characteristics, in-cylinder flow, operation & engine parameters and fuel composition is a major factor. The goal of this paper is to evaluate the influence of different biogenic and alkylate fuels on the gaseous and particle number emission behavior during catalyst heating operation on a single-cylinder DISI engine. The engine is operated with a late ignition timing causing a high exhaust enthalpy flow to heat up the catalyst, a slightly lean global air fuel ratio to avoid high hydrocarbon emissions and a late injection right before the ignition to reduce the coefficient of variance of the indicated mean effective pressure.

The two-stroke SI engine is the predominant driving unit in applications that require a high power-to-weight ratio, such as handheld power tools. Regarding the latest regulations in emission limits the main development area is clearly a further reduction of the exhaust emissions. The emissions are directly linked to the combustion processes and the scavenging losses. The optimization of the combustion processes, which represents one of the most challenging fields of research, is still one of the most important keys to enhance the thermal efficiency and reduce exhaust emissions. Regarding future emission regulations for small two-stroke SI engines it is inevitable that the emissions of gases causing the greenhouse effect, like carbon dioxide, need to be reduced. As most small SI engines are carburetted and operate open loop, the mixture formation and the amount of residual gas differs from cycle to cycle [1].

Diesel engines face difficult challenges with respect to engine-out emissions, efficiency and power density as the legal requirements concerning emissions and fuel consumption are constantly increasing. In general, for a diesel engine to achieve low raw emissions a well-mixed fuel-air mixture, burning at low combustion temperatures, is necessary. Highly premixed diesel combustion is a feasible way to reduce the smoke emissions to very low levels compared to conventional diesel combustion. In order to reach both, very low NOX and soot emissions, high rates of cooled EGR are necessary. With high rates of cooled EGR the NOX formation can be suppressed almost completely. This paper investigates to what extent the trade-off between emissions, fuel consumption and power of a diesel engine can be resolved by highly premixed and low temperature diesel combustion using injection nozzles with reduced injection hole diameters and high pressure fuel injection.

The focus of this work was to determine the influence of spray targeting on temperature distributions, combustion progress and unburned hydrocarbon (HC) emissions at cold operating conditions, and to show the capability of model and full engine tests adapted for different measurement techniques. A comprehensive study applying endoscopic visualization, infrared thermography, combustion and emission measurements was carried out in a 4-stroke 4-cylinder 16-valve production engine with intake port injection during different engine operating conditions including injection angle and timing. In addition 2D visualization and PIV measurements were performed in a back-to-back model test section with good optical access to the intake manifold and the combustion chamber. The measurements in both set ups were in good agreement and show that model tests could lead to useful findings for a real engine.

E-fuels are proven to be a major contributing factor to reduce CO2 emissions in internal combustion engines. In gasoline engines, C1 oxygenate are seen as critical to reach CO2 and emission reduction goals. Their properties affect the fuel injection characteristics and thus the fuel mixture formation and combustion emissions. To exploit the full potential of e-fuels, the detailed knowledge of their spray characteristic is necessary. The correlation between the fuel content of C1 oxygenates and particulate emissions do not appear to be linear. To understand this correlation, the spray characteristics have to be investigated in detail. The reduced stoichiometric air requirement leads to an increase of the injected fuel mass, which has to evaporate. This can lead to a changed fuel film interaction within the combustion chamber walls and therefore a change of particle formation.