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The present work is a continuation of the earlier published results by authors on the investigation of Hydrogenated Vegetable Oil (HVO) on a High Efficiency Diesel Combustion System (SAE Int. J. Fuels Lubr. Paper No. 2013-01-1677 and JSAE Paper No. 283-20145128). In order to further validate and interpret the previously published results of soot microstructure and its consequences on oxidation behavior, the test program was extended to analyze the impact of soot composition, optical properties, and physical properties such as size, concentration etc. on the oxidation behavior. The experiments were performed with pure HVO as well as with petroleum based diesel and today's biofuel (i.e. FAME) as baseline fuels. The soot samples for the different analyses were collected under constant engine operating conditions at indicated raw NOx emissions of Euro 6 level using closed loop combustion control methodology.

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.

Within the Cluster of Excellence “Tailor-Made Fuels from Biomass” at RWTH Aachen University, the Institute for Combustion Engines carried out an investigation program to explore the potential of future biofuel components in Diesel blends. In this paper, thermodynamic single cylinder engine results of today's and future biofuel components are presented with respect to their engine-out emissions and engine efficiency. The investigations were divided into two phases: In the first phase, investigations were performed with rapeseed oil methyl ester (B100) and an Ethanol-Gasoline blend (E85). In order to analyze the impact of different fuel blends, mixtures with 10 vol-% of B100 or E85 and 90 vol-% of standardized EN590 Diesel were investigated. Due to the low cetane number of E85, it cannot be used purely in a Diesel engine.

In order to deeply investigate and improve the complete path from biofuel production to combustion, the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University in 2007. Recently, new pathways have been discovered to synthesize octanol [1] and di-n-butylether (DNBE). These molecules are identical in the number of included hydrogen, oxygen and carbon atoms, but differ in the molecular structure: for octanol, the oxygen atom is at the end of the molecule, whereas for DNBE it is located in the middle. In this paper the utilization of octanol and DNBE in a state-of-the-art single cylinder diesel research engine will be discussed. The major interest has been on engine emissions (NOx, PM, HC, CO, noise) compared to conventional diesel fuel.

Downsized direct-injected boosted gasoline engines with high specific power and torque output are leading the way to reduce fuel consumption in passenger car vehicles while maintaining the same performance when compared to applications with larger naturally aspirated engines. These downsized engines reach brake mean effective pressure levels which are in excess of 20 bar. When targeting high output levels at low engine speeds, undesired combustion events called pre-ignition can occur. These pre-ignition events are typically accompanied by very high cylinder peak pressures which can lead to severe damage if the engine is not designed to withstand these high cylinder pressures. Although these pre-ignition events have been reported by numerous other authors, it seems that their occurrence is rather erratic which makes it difficult to investigate or reliably exclude them.

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.

Pre-ignition in a boosted spark-ignition engine can be triggered by several mechanisms, including oil-fuel droplets, deposits, overheated engine components and gas-phase autoignition of the fuel-air mixture. A high pre-ignition resistance of the fuel used mitigates the risk of engine damage, since pre-ignition can evolve into super-knock. This paper presents the pre-ignition propensities of 11 RON 89-100+ gasoline fuel blends in a single-cylinder research engine. Albeit the addition of two high-octane components (methanol and reformate) to a toluene primary reference fuel improved the pre-ignition resistance, one high-RON fuel experienced runaway pre-ignition at relatively low boost pressure levels. A comparison of RON 96 blends showed that the fuel composition can affect pre-ignition resistance at constant RON.

Based on the TurboDISI engine presented earlier [1], [2], a new Spray Guided Turbo (SGT) concept with enhanced engine performance was developed. The turbocharged engine was modified towards utilizing a spray-guided combustion system with a central piezo injector location. Higher specific power and torque levels were achieved by applying specific design and cooling solutions. The engine was developed utilizing a state-of-the-art newly developed charge motion design (CMD) process in combination with single cylinder investigations. The engine control unit has a modular basis and is realized using rapid prototyping hardware. Additional fuel consumption potentials can be achieved with high load EGR, use of alternative fuels and a hybrid powertrain. The CO2 targets of the EU (120 g/km by 2012 in the NEDC) can be obtained with a mid-size vehicle applying the technologies presented within this paper.

Today's biofuels require large amounts of energy in the production process for the conversion from biomass into fuels with conventional properties. To reduce the amounts of energy needed, future fuels derived from biomass will have a molecular structure which is more similar to the respective feedstock. Butyl levulinate can be gained easily from levulinic acid which is produced by acid hydrolysis of cellulose. Thus, the Institute for Combustion Engines at RWTH Aachen University carried out a fuel investigation program to explore the potential of this biofuel compound, as a candidate for future compression ignition engines to reduce engine-out emissions while maintaining engine efficiency and an acceptable noise level. Previous investigations identified most desirable fuel properties like a reduced cetane number, an increased amount of oxygen content and a low boiling temperature for compression ignition engine conditions.

Lignocellulosic biomass consists of (hemi-) cellulose and lignin. Accordingly, an integrated biorefinery will seek to valorize both streams into higher value fuels and chemicals. To this end, this study evaluated the overall combustion performance of both cellulose- and lignin derivatives, namely the high cetane number (CN) di-n-butyl ether (DnBE) and low CN anisole, respectively. Said compounds were blended both separately and together with EN590 diesel. Experiments were conducted in a single cylinder compression ignition engine, which has been optimized for improved combustion characteristics with respect to low emission levels and at the same time high fuel efficiency. The selected operating conditions have been adopted from previous “Tailor-Made Fuels from Biomass (TMFB)” work.

In order to thoroughly investigate and improve the path from biofuel production to combustion, the Cluster of Excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University in 2007. Since then, a variety of fuel candidates have been investigated. In particular, 2-methyl tetrahydrofurane (2-MTHF) has shown excellent performance w.r.t. the particulate (PM) / NOx trade-off [1]. Unfortunately, the long ignition delay results in increased HC-, CO- and noise emissions. To overcome this problem, the addition of di-n-butylether (DNBE, CN ∼ 100) to 2-MTHF was analyzed. By blending these two in different volumetric shares, the effects of the different mixture formation and combustion characteristics, especially on the HC-, CO- and noise emissions, have been carefully analyzed. In addition, the overall emission performance has been compared to EN590 diesel.

Modern biofuels offer the potential to decrease engine out emissions while at the same time contributing to a reduction of greenhouse gases produced from individual mobility. In order to deeply investigate and improve the complete path from biofuel production to combustion, in 2007 the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University. Since then, a whole variety of possible fuel candidates have been identified and investigated. In particular oxygenated fuels (e.g. alcohols, furans) have proven to be beneficial regarding the particulate matter (PM)/ NOx trade-off [1, 2, 3] in diesel-type combustion. Alcohols that provide a longer ignition delay than diesel might behave even better with regard to this trade-off due to higher homogenization of the mixture. Recent studies carried out within the Cluster of Excellence have discovered new pathways to derive 1-octanol from biomass [4], which features a derived cetane number (DCN) of 39.

Oxygenated fuels such as polyoxymethylene dimethyl ethers (OME) offer a chance to significantly decrease emissions while switching to renewable fuels. However, compared to conventional diesel fuel, they have lower heating values and different evaporation behaviors which lead to differences in spray, mixture formation as well as ignition delay. In order to determine the mixture formation characteristics and the combustion behavior of neat OME3-5, optical investigations have been carried out in a high-pressure-chamber using shadowgraphy, mie-scatterlight and OH-radiation recordings. Liquid penetration length, gaseous penetration length, lift off length, spray cone angle and ignition delay have been determined and compared to those measured with diesel-fuel over a variety of pressures, temperatures, rail pressures and injection durations.

Downsizing of highly-boosted spark-ignition (SI) engines is limited by pre-ignition, which may lead to extremely strong knocking and severe engine damage. Unfortunately, the concerning mechanisms are generally not yet fully understood, although several possible reasons have been suggested in previous research. The primary objective of the present paper is to investigate the influence of molecular bio-fuel structure on the locations of pre-ignition in a realistic, highly-charged SI engine at low speed by state-of-the-art optical measurements. The latter are conducted by using a high-sensitivity UV endoscope and an intensified high-speed camera. Two recently tested bio-fuels, namely tetrahydro-2-methylfuran (2-MTHF) and 2-methylfuran (2-MF), are investigated. Compared to conventional fuels, they have potential advantages in the well-to-tank balance. In addition, both neat ethanol and conventional gasoline are used as fuels.

The current and future restrictions on pollutant emissions from internal combustion engines require a holistic investigation of the abilities of alternative fuels to optimize the combustion process and ensure cleaner combustion. In this regard, the Tailor-made Fuels from Biomass (TMFB) Cluster at Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University aims at designing production processes for biofuels as well as fuels optimal for use in internal combustion engines. The TMFB Cluster's scientific approach considers the molecular structure of the fuels as an additional degree of freedom for the optimization of both the production pathways and the combustion process of such novel biofuels. Thus, the model-based specification of target parameters is of the utmost importance to improve engine combustion performance and to send feedback information to the biofuel production process.

Numerical analyses of the liquid fuel injection and subsequent fuel-air mixing for a high-tumble direct injection engine with an active pre-chamber ignition system at operation conditions of 2000 RPM are presented. The Navier-Stokes equations for compressible in-cylinder flow are solved numerically using a hierarchical Cartesian mesh based finite-volume method. To determine the fuel vapor before ignition large-eddy flow simulations are two-way coupled with the spray droplets in a Lagrangian Particle Tracking (LPT) formulation. The combined hierarchical Cartesian mesh ensures efficient usage of high performance computing systems through solution adaptive refinement and dynamic load balancing. Computational meshes with approximately 170 million cells and 1.0 million spray parcels are used for the simulations.

Maintaining low NOx emissions over the operating range of diesel engines continues to be a major issue. However, optical measurements of nitric oxide (NO) are lacking particularly in the core of diesel jets, i.e. in the region of premixed combustion close to the spray axis. This is basically caused by severe attenuation of both the laser light and fluorescent emission in laser-induced fluorescence (LIF) applications. Light extinction is reduced by keeping absorption path lengths relatively short in this work, by investigating diesel jets in a combustion vessel instead of an engine. Furthermore, the NO-detection threshold is improved by conducting 1-d line measurements instead of 2-d imaging. The NO-LIF data are corrected for light attenuation by combined LIF and spontaneous Raman scattering. The quantified maximum light attenuation is significantly lower than in comparable previous works, and its wavelength dependence is surprisingly weak.

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.

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.