Search Results

Due to increasingly strict emission regulations, the demand for internal combustion engine performance has enhanced. Combustion stability is one of the main research focuses due to its impacts on the emission level. Moreover, the combustion instability becomes more significant under the lean combustion concept, which is an essential direction of internal combustion engine development. The combustion instability is represented as the cycle-to-cycle variation. This paper presents a quasi-dimensional model system for predicting the cycle-to-cycle variation in 0D/1D simulation. The modeling is based on the cause-and-effect chain of cycle-to-cycle variation of spark ignition engines, which is established through the flow field analysis of large eddy simulation results [1]. In the model system, varying parameters are turbulent kinetic energy, the distribution of air-to-fuel equivalence ratio, and the in-cylinder velocity field.

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.

The dilution of the cylinder charge using excess air enables both an increase in the net indicated efficiency and a decrease in the engine-out emissions of nitrogen oxides. The maximum excess air dilution capability in a spark-ignition engine depends on both the ignition of the charge and the flame propagation. These two aspects can be influenced by the fuel properties, which draw attention to the laminar burning velocity of alternative fuels to extend the lean limit. Cyclopentanone and anisole show promising values regarding the laminar burning velocity. However, there is a lack of engine investigations using these two fuels. To this end, both fuels were assessed in an engine application using experimental and numerical investigations. Cyclopentanone and anisole were investigated as neat components and as mixtures with conventional gasoline fuel, resulting in seven investigated fuels.

State-of-the-art spark-ignition engines mainly rely on the quasi-hemispherical flame propagation combustion method. Despite significant development efforts to obtain high energy conversion efficiencies while avoiding knock phenomena, achieved indicated efficiencies remain around 35 - 40 %. Further optimizations are enabled by significant excess air dilution or increased combustion speed. However, flammability limits and decreasing flame speeds with increasing air dilution prevent substantial improvements. Pre-Chamber (PC) initiated jet ignition combustion systems improve flame stability and shift flammability limits towards higher dilution levels due to increased turbulence and a larger flame area in the early Main-Chamber (MC) combustion stages. Simultaneously, the much-increased combustion speed reduces knock tendency, allowing the implementation of an innovative combustion method: PC-initiated jet ignition coupled with Spark-Assisted Compression Ignition (SACI).

Prospective combustion engine applications require the highest possible energy conversion efficiencies for environmental and economic sustainability. For conventional Spark-Ignition (SI) engines, the quasi-hemispherical flame propagation combustion method can only be significantly optimized in combination with high excess air dilution or increased combustion speed. However, with increasing excess air dilution, this is difficult due to decreasing flame speeds and flammability limits. Pre-Chamber (PC) initiated jet ignition combustion systems significantly shift the flammability and flame stability limits towards higher dilution areas due to high levels of introduced turbulence and a significantly increased flame area in early combustion stages, leading to considerably increased combustion speeds and high efficiencies. By now, vehicle implementations of PC-initiated combustion systems remain niche applications, especially in combination with lean mixtures.

The increasingly stringent limits on pollutant emissions from internal combustion engine-powered vehicles require the optimization of advanced combustion systems by means of virtual development and simulation tools. Among the gaseous emissions from spark-ignition engines, the unburned hydrocarbon (HC) emissions are the most challenging species to simulate because of the complexity of the multiple physical and chemical mechanisms that contribute to their emission. These mechanisms are mainly three-dimensional (3D) resulting from multi-phase physics - e.g., fuel injection, oil-film layer, etc. - and are difficult to predict even in complex 3D computational fluid-dynamic (CFD) simulations. Phenomenological models describing the relationships between the physical-chemical phenomena are of great interest for the modeling and simplification of such complex mechanisms.

Homogeneous charge compression ignition (HCCI) is a part load, low-temperature combustion process which operates at lean mixtures and produces ultra-low NOX emissions. As opposed to SI engines that use a spark to control combustion timing, HCCI combustion is enabled by compression induced autoignition which is characterized by rapid global and spatial combustion yielding fuel efficiency benefits. This process is highly dependent on the in-cylinder state, including pressure, temperature and trapped mass. The absence of a direct combustion control proves to be a major challenge and results in unstable engine operation especially at the limits of the narrow operation range. In recent studies, direct water injection is used in HCCI combustion to stabilize combustion and increase the operation range. This paper outlines the thermodynamic influence and evaluation of the potential of water injection for HCCI combustion.

The development and validation of detailed simulation models of in-cylinder combustion, emission formation mechanisms and reaction kinetics in the exhaust system are of crucial importance for the design of future low-emission powertrain concepts. To investigate emission formation mechanisms on one side and to create a solid basis for the validation of simulation methodologies (e.g. 3D-CFD, multi-dimensional in-cylinder models, etc.) on the other side, specific detailed measurements in the exhaust system are required. In particular, the hydrocarbon (HC) emissions are difficult to be investigated in simulation and experimentally, due to their complex composition and their post-oxidation in the exhaust system. In this work, different emission measurement devices were used to track the emission level and composition at different distances from the cylinder along the exhaust manifold, from the exhaust valve onwards.

Two-stage variable compression ratio (VCR) systems for spark ignited engines offer a CO2 reduction potential of approx. 5%. Due to their modularity, connecting rod based VCR-systems can be integrated into existing engine assembly systems, where engines can be built in parallel with or without such a system, depending on performance and market requirements. In order to comply with the new RDE emission standards with high specific power engine variants, VCR systems enable high load engine operation without fuel enrichment. The interactions between the hydraulic-, mechanical - and oil supply systems of a VCR-system with variable connecting rod length are complex and require a well-developed and adapted layout of all subsystems. This demands the use of tailored measurement and simulation tools during the development and application phases. In this context, Advanced Functional Pulse Testing enables single-parameter analyses of VCR con rods.

Liquefied Petroleum Gas direct injection (LPG DI) is believed to be the key enabler for the adaption of modern downsized gasoline engines to the usage of LPG, since LPG DI avoids the significant low end torque drop, which goes along with the application of conventional LPG port fuel injection systems to downsized gasoline DI engines, and provides higher combustion efficiencies. However, especially the high vapor pressure of C3 hydrocarbons can result in hot fuel handling issues as evaporation or even in reaching the supercritical state of LPG upstream or inside the high pressure pump (HPP). This is particularly critical under hot soak conditions. As a result of a rapid fuel density drop close to the supercritical point, the HPP is not able to keep the rail pressure constant and the engine stalls.

Due to their CO2 reduction potential and their high knock resistance gaseous fuels present a promising alternative for modern highly boosted spark ignition engines. Especially the direct injection of LPG reveals significant advantages. Previous studies have already shown the highest thermodynamic potential for the LPG direct injection concept and its advantages in comparison to external mixture formation systems. In the performed research study a comparison of different LPG fuels in direct injection mode shows that LPG fuels have better auto-ignition behavior than gasoline. A correlation between auto-ignition behavior and the calculated motor octane number could not be found. However, a significantly higher correlation of R2 = 0.88 - 0.99 for CR13 could be seen when using the methane number. One major challenge in order to implement the LPG direct injection concept is to ensure the liquid state of the fuel under all engine operating conditions.

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.

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.

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 requirement of reducing worldwide CO₂ emissions and engine pollutants are demanding an increased use of bio-fuels. Ethanol with its established production technology can contribute to this goal. However, due to its resistive auto-ignition behavior the use of ethanol-based fuels is limited to the spark-ignited gasoline combustion process. For application to the compression-ignited diesel combustion process advanced ignition systems are required. In general, ethanol offers a significant potential to improve the soot emission behavior of the diesel engine due to its oxygen content and its enhanced evaporation behavior. In this contribution the ignition behavior of ethanol and mixtures with high ethanol content is investigated in combination with advanced ignition systems with ceramic glow-plugs under diesel engine relevant thermodynamic conditions in a high pressure and temperature vessel.

Partly competing objectives, as low fuel consumption, low friction, long oil maintenance rate, and at the same time lowest exhaust emissions have to be fulfilled. Diminishing resources, continuously reduced development periods, and shortened product cycles yield detailed knowledge about oil consumption mechanisms in combustion engines to be essential. There are different ways for the lubricating oil to enter the combustion chamber: for example as blow-by gas, leakage past valve stem seals, piston rings (reverse blow-by) and evaporation from the cylinder liner wall and the combustion chamber. For a further reduction of oil consumption the investigation of these mechanisms has become more and more important. In this paper the influence of the mixture formation and the resulting fuel content in the cylinder liner wall film on the lubricant oil emission was examined.

Advanced technologies such as direct injection DI, turbocharging and variable valve timing, have lead to a significant evolution of the gasoline engine with positive effects on driving pleasure, fuel consumption and emissions. Today's developments are primarily focused on the implementation of improved full load characteristics for driving performance and fuel consumption reduction with stoichiometric operation, following the downsizing approach in combination with turbocharging and high specific power. The requirements of a relatively small cylinder displacement with high specific power and a wide flexibility of DI injection specifications lead to competing development targets and additionally to a high number of degrees of freedom during optimization. In order to successfully approach an optimum solution, FEV has evolved an advanced development methodology, which is based on the combination of simulation, optical diagnostics and engine thermodynamics testing.

Fuels derived from biomass will most likely contain oxygen due to the high amount of hydrogen needed to remove oxygen in the production process. Today, alcohol fuels (e. g. ethanol) are well understood for spark ignition engines. The Institute for Combustion Engines at RWTH Aachen University carried out a fuel investigation program to explore the potential of alcohol fuels as candidates for future compression ignition engines to reduce engine-out emissions while maintaining engine efficiency and an acceptable noise level. The soot formation and oxidation process when using alcohol fuels in diesel engines is not yet sufficiently understood. Depending on the chain length, alcohol fuels vary in cetane number and boiling temperature. Decanol possesses a diesel-like cetane number and a boiling point in the range of the diesel boiling curve. Thus, decanol was selected as an alcohol representative to investigate the influence of the oxygen content of an alcohol on the combustion performance.

The finite nature and instability of fossil fuel supply has led to an increasing and enduring investigation demand of alternative and regenerative fuels. The Institute for Combustion Engines at the RWTH Aachen University carried out an investigation program to explore the potential of tailor made fuels to reduce engine-out emissions while maintaining engine efficiency and an acceptable noise level. To enable optimum engine performance a range of different hydrocarbons having different fuel properties like cetane number, boiling temperature and different molecular compositions have been investigated. Paraffines and naphthenes were selected in order to better understand the effects of molecular composition and chain length on emissions and performance of an engine that was already optimized for advanced combustion performance. The diesel single-cylinder research engine used in this study will be used to meet Euro 6 emissions limits and beyond.

Increasing shortages of energy resources as well as emission legislation is increasing the pressure to develop more efficient, environmentally friendly propulsion systems for vehicles. Due to its more than 125 years of history with permanent improvements, the internal combustion engine (ICE) has reached a very high development status in terms of efficiency and emissions, but also drivability, handling and comfort. Therefore, the IC engine will be the dominant propulsion system for future generations. This paper gives a survey on the present technical status and future prospects of internal combustion engines, both CI and SI engines, also including alternative fuels. In addition a brief overview of the potential of currently intensely discussed hybrid concepts is given.