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Downsizing is an effective way to further improve the efficiency of SI engines. To make most of this concept, the compression ratio has to be adjusted during engine operation. Thus, the efficiency disadvantages during part load can be eliminated. A fuel consumption reduction of up to 30% can be realized compared to naturally aspirated engines of the same power. After the assessment of several known concepts it turned out that the eccentric crankshaft positioning represents an appropriate solution which meets the requirements of good adjustability, unaltered inertia forces, low power demand of the positioning device and reasonable design effort. The basic challenges posed by the eccentric crankshaft positioning have been tackled, namely the crankshaft bearing and the integration of the newly developed power take-offs which have almost no influence on the base design.

Experiments were conducted on a turbocharged three cylinder automotive common rail diesel engine with port injection of butanol. This dual fuel engine was run with neat butanol and blends of water and butanol (up to 20% water by mass). Experiments were performed at a constant speed of 1800 rpm and a brake mean effective pressure of 11.8 bar (full load) at varying butanol to diesel energy share values while diesel was either injected as a single pulse or as twin pulses (Main plus Post). Open engine controllers were used for varying the injection parameters of diesel and butanol. Water butanol blends improved the brake thermal efficiency by a small extent because of better combustion phasing as compared to butanol without water. When the butanol to diesel energy share was high, auto-ignition of butanol occurred before the injection of diesel. This lowered the ignition delay of diesel and hence elevated the smoke level.

The main assignment of Controlled Auto Ignition (CAI) operation range expansion is to reduce the burn rate or combustion noise at high load and to minimize misfire at low load. The potential of two principal EGR strategies is well known to initiate CAI in a wide range of operation map by using a variable train system: the Exhaust Port Recirculation (EPR) for higher part load and the Combustion Chamber Recirculation (CCR - also called Negative Valve Overlap) for lower part load. However the detailed comparison of the ignition phenomena with each EGR strategy has not been fully studied yet. In this paper, EPR and CCR were compared with same operational condition (engine speed and load). For the analysis, flame luminescence and Raman scattering method for optical measurement and STAR-CD (CD-adapco) for numerical simulation are used.

By variation of the compression ratio the fuel consumption of high boosted gasoline engines can be reduced, due to operating with higher compression ratios at low load compared to an engine with fixed compression ratio. The two-stage VCR-system enables a high share of fuel saving potential relative to full variable systems. Considering a low cost manufacturability and a beneficial integratability into common engine architectures the length-adjustable conrod using an eccentric piston pin in the small eye has proved as the best concept. The adjustment is performed by a combination of gas and mass forces. This article describes the design of such a two-stage VCR-system as well as the functional testing under motored and fired engine operating conditions.

The demand for fuel-efficient, low-displacement engines for future passenger car applications led to investigations with small DI diesel engines in the advanced engineering department at Mercedes-Benz. Single-cylinder tests were carried out to compare a 2-valve concept with 241 cm3 displacement with a 422 cm3 4-valve design, both operated with a common rail injection system. Mean effective pressures at full load were about 10 % lower with the smaller displacement. With such engines a specific power of 40 kW/I and a specific torque of about 140 Nm/I should be possible. In the current stage of optimization, penalties in fuel economy could be reduced down to values below 3 %. The “4-cylinder DI diesel engine with 1 liter displacement” is an interesting alternative to small 3 cylinder concepts with higher displacement per cylinder. An introduction into series production will not only depend on the potential for further improvement in fuel economy of such small cylinder units.

Mass-production single-cylinder engines are generally not turbocharged due to pulsated exhaust flow. Hence, about one-third of the fuel chemical energy is wasted in the engine exhaust. To extract the exhaust energy and boost the single-cylinder engines, a novel supercharging with a turbo-compounding strategy is proposed in the present work, wherein an impulse turbine extracts energy from the pulsated exhaust gas flow. Employing an impulse turbine for a vehicular application, especially on a single-cylinder engine, has never been commercially attempted. Hence, the design of the impulse turbine assumes higher importance. A nozzle, designed as a stator part of the impulse turbine and placed at the exhaust port to accelerate the flow velocity, was included as part of the layout in the present work. The layout was analyzed using the commercial software AVL BOOST. Different nozzle exit diameters were considered to analyze their effect on the exhaust back pressure and engine performance.

High levels of exhaust temperature or rich mixtures are necessary for the regeneration of today's diesel particulate filters or NOx catalysts. Therefore, late main injection or post injection is an effective strategy but leads to the well-known problem of lubricating oil dilution depending on the geometry, rail pressure and injection strategy. In this paper a method is developed to simulate fuel entrainment into the lubricating oil wall film in the diesel combustion chamber to predict oil dilution in an early design stage prior to hardware availability for durability testing. The simulation method integrates a newly developed droplet-film interaction model and is compared to results of an optical single-cylinder diesel engine and a similar thermodynamic single-cylinder test engine. Phenomena of diesel post injection like igniting early post injection or split post injections with short energizing times are considered in this paper.

Methanol has a very low cetane number but it can be used in the neat form in a glow plug based hot surface ignition (HSI) engine at CI engine compression ratios. A CFD simulation model of a glow plug assisted methanol HSI engine was developed and validated using experimental data reported in literature. A study on the effect of single and multipulse injection of methanol, glow plug surface temperature, injection pressure and effect of shielding it were conducted by applying the model on to a three cylinder neat methanol HSI engine. A glow surface temperature of 1273 K was found to be sufficient for ignition of methanol at 50% load while the distance between the glow plug and the injector affected the ignition delay. The sprays were ignited sequentially starting from the one closest the glow plug which resulted in extended combustion. Injecting methanol in double pulses reduced the Maximum Rate of Pressure Rise (MRPR).

The continuously strengthened requirements regarding air quality and pollutant reduction as well as GHG emissions further complicate the compliance with legal standards. Especially in view of cost-sensitive applications this demand strongly collides with the EMS set-up and the sensor requirements with still increasing overall system complexity. The paper in hand describes a novel air path control approach, which offers the potential for a flexible use of multiple EGR routes to meet upcoming legislations more robustly, while providing a significant reduction of calibration effort and sensor content at the same time. By using a direct emission based cylinder charge control, also alterations in operational ambient conditions are covered with system reactions according to physical-based rules to enhance the engine-out emission performance without need for tuning of corrections of any air path set point.

Fuel properties are always considered as one of the main factors to diesel engines concerning performance and emission discussions. There are still challenges for researchers to identify the most correlating and non-correlating fuel properties and their effects on engine behavior. Statistical analyses have been applied in this study to derive the most un-correlating properties. In parallel, sensitivity analysis was performed for the fuel properties as well as to the emission and performance of the engine. On one hand, two different analyses were implemented; one with consideration of both, non-aromatic and aromatic fuels, and the other were performed separately for each individual fuel group. The results offer a different influence on each type of analysis. Finally, by considering both methods, most common correlating and non-correlating properties have been derived.

The use of pistons made of fine grain carbon was investigated in a spark-ignition engine within a European Community funded research project (TPRO-CT92-0008). Pistons were designed and manufactured and then tested in a single cylinder engine. Due to the carbon material's lower coefficient of thermal expansion the top land clearance between piston and cylinder can be reduced by a factor of three in comparison to standard aluminium designs. Under steady-state part-load operating conditions the emission of unburned hydrocarbons can be reduced by more than 15% compared to aluminium pistons, without significant penalties in NOx-emissions. Simultaneously, a small improvement in fuel economy of about 2% is observed. At full-load blow-by leakage flow is reduced by more than 50%. The piston crown temperature is about 30°C higher with the carbon piston than with the standard aluminium piston, due to the lower thermal conductivity of the carbon material.

In this paper a new approach is presented to evaluate the combustion behaviour of homogeneous gasoline engines by predicting burn delay and -duration in a way which can be obtained under the time constraints of the development process. This is accomplished by means of pure in-cylinder flow simulations without a classical combustion model. The burn delay model is based on the local distribution of the turbulent flow near the spark plug. It features also a methodology to compare different designs regarding combustion stability. The correlation for burn duration uses a turbulent characteristic number that is obtained from the turbulent flow in the combustion chamber together with a model for the turbulent burning velocity. The results show good agreement with the combustion process of the analyzed engines.

For turbocharged engines high specific power and torque output as well as a fast transient response are mandatory. This conflict of aims can be solved by different charging systems, for example 2-stage charging or variable turbine geometry. At the Institute for Combustion Engines (VKA) at RWTH Aachen University another alternative, the variable compressor pre swirl, was investigated for solving this conflict of aims. Based on theoretical fundamentals the potentials of a variable compressor pre swirl for transient response, low end torque, specific power output and fuel consumption were presented. These theoretical potentials were explored on turbocharger -, engine - and vehicle test bench. An extended compressor map with partial higher compressor efficiency of up to 2% was detected. The outcome of this is an increase of up to 6% in low end torque, found on engine test bench. This effect could also be validated in 1D simulation.

The current direction for Diesel combustion system development is towards homogenization, in order to reduce particulate and NOx emissions. However, a strong increase of carbon monoxide emissions (CO) is frequently noted in combination with enhanced homogenization. Therefore, the current investigation focuses on a detailed analysis of the particulate - CO trade-off using a laser-optical and multidimensional CFD investigation of the combustion process of a swirl HSDI system. The CFD methodology involves reduced kinetics for soot formation and oxidation and a three-step CO model. These models are validated by a detailed comparison to optical measurements of flow, spray penetration and the spatial distribution of soot, temperature and oxygen concentration. The results obtained show that high concentrations of CO occur as an intermediate combustion reaction product. Subsequently, CO and soot are oxidized in large areas of the combustion chamber.

Most of today’s internal combustion engines are turbocharged by combined radial compressors and turbines for downsizing. This mostly leads to reduced orifice noise of both intake and exhaust systems, but the detailed damping mechanisms remain yet unknown. Intake and exhaust systems are developed with 1D-CFD simulations, but validated acoustic sub-models for turbochargers are not yet available. Therefore the aim of this publication is studying the turbocharger’s silencing capabilities and subsequently develop new acoustic turbocharger models. The acoustic properties of the turbocharger can be well described by transmission loss. In addition to thermodynamic variations, parameter variations with wastegate and VTG systems were also performed. A total of four turbochargers of very different sizes were investigated. Low frequency attenuation is dominated by impedance discontinuities, increasing considerably with mass flow and pressure ratio.

With increasing interest in new biofuel candidates, 1-octanol and di-n-butylether (DNBE) were presented in recent studies. Although these molecular species are isomers, their properties are substantially different. In contrast to DNBE, 1-octanol is almost a gasoline-type fuel in terms of its auto-ignition quality. Thus, there are problems associated with engine start-up for neat 1-octanol. In order to find a suitable glow-plug position, mixture formation is studied in the cylinder under almost idle operating conditions in the present work. This is conducted by planar laser-induced fluorescence in a high-speed direct-injection optical diesel engine. The investigated C8-oxygenates are also significantly different in terms of their evaporation characteristics. Thus, in-cylinder mixture formation of these two species is compared in this work, allowing conclusions on combustion behavior and exhaust emissions.

The influence of two oxygenated tailor-made fuels on soot formation and oxidation in an optical single cylinder research diesel engine has been studied. For the investigation a planar laser-induced incandescence (PLII) measurement technique was applied to the engine in order to detect and evaluate the planar soot distribution for the two bio fuels within a laser light sheet. Furthermore the OH* chemiluminescence and broad band soot luminosity was visualized by high speed imaging to compare the ignition and combustion behavior of tested fuels: Two C8 oxygenates, di-n-butylether (DNBE) and 1-octanol. Both fuels have the same molecular formula but differ in their molecular structure. DNBE ignites fast and burns mostly diffusive while 1-octanol has a low cetane number and therefore it has a longer ignition delay but a more homogeneous mixture at time of ignition. The two bio fuels were finally compared to conventional diesel fuel.

Single-cylinder engines in mass production are generally not turbocharged due to the pulsated and intermittent exhaust gas flow into the turbocharger and the phase lag between the intake and exhaust stroke. The present work proposes a novel approach of decoupling the turbine and the compressor and coupling them separately to the engine to address these limitations. An impulse turbine is chosen for this application to extract energy during the pulsated exhaust flow. Commercially available AVL BOOST software was used to estimate the overall engine performance improvement of the proposed novel approach compared to the base naturally aspirated (NA) engine. Two different impulse turbine layouts were analyzed, one without an exhaust plenum and the second layout having an exhaust plenum before the power turbine. The merits and limitations of both layouts are compared in the present study.

Despite the advantages of turbocharging in improved engine performance and reduced exhaust emissions, commercial single-cylinder engines used for automotive applications remain naturally aspirated (NA) and are not generally turbocharged. This is due to the shortcomings with pulsated and intermittent exhaust gas flow into the turbine and the phase lag between the intake and exhaust stroke. In the present study, experimental investigations are initially carried out with a suitable turbocharger closely coupled to a single-cylinder diesel engine. Results indicated that the engine power dropped significantly by 40% for the turbocharged engine compared to the NA version even though the air mass flow rate was increased by at least 1.5 times with turbocharging. A novel approach of decoupling the turbine and the compressor and coupling them separately to the engine is proposed to address these limitations.

The purpose of this study is to investigate the effect of spray-bowl interaction on combustion, and pollutants formation at one specific high-load point of a single-cylinder small-bore diesel engine through computational analysis. The simulations are performed using Representative Interactive Flamelet (RIF) model with detailed chemical kinetics. Detailed chemistry-based soot model is used for the prediction of soot emissions. The simulations are performed for five different injection timings. Model-predicted cylinder pressure and exhaust emissions are validated against the measured data for all the injection timings. A new method - Two-part analysis - is then applied to investigate the spray-bowl interaction. Two-part analysis splits the volume of the combustion chamber into two, namely the piston bowl and the squish volume. Through analysis, among others the histories of soot, carbon monoxide (CO) and nitric oxide (NO ) emissions inside both volumes are shown.