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Technical Paper

An Experimental Investigation of Combustion and Soot Formation of Sprays from Cluster Nozzles for DI Diesel Engines

One of the basic topics in the design of new injection systems for DI Diesel engines is to decrease the soot emissions. A promising approach to minimize soot production are nozzles with clustered holes. A basic idea of the Cluster Configuration (CC) nozzles is to prevent a fuel rich area in the center of the flame where most of the soot is produced, and to minimize the overall soot formation in this way. For this purpose each hole of a standard nozzle is replaced by two smaller holes. The diameter of the smaller holes is chosen so that the flow rate of all nozzles should be equal. The basic strategy of the cluster nozzles is to provide a better primary break up and therefore a better mixture formation caused by the smaller nozzle holes, but a comparable penetration length of the vapor phase due to merging of the sprays. Three possible arrangements of the clustered holes are investigated in this study. Both the cluster angle and the orientation to the injector axis are varied.
Technical Paper

Analysis of the Emission Conversion Performance of Gasoline Particulate Filters Over Lifetime

Gasoline particulate filters (GPF) recently entered the market, and are already regarded a state-of-the-art solution for gasoline exhaust aftertreatment systems to enable EU6d-TEMP fulfilment and beyond. Due to their rapid market introduction, extensive field experience with GPFs is not yet available. Especially for four-way catalytic converters, the prognosis of the emission conversion performance over lifetime poses an ambitious challenge, which significantly influences future catalyst diagnosis calibrations. In the first part of the paper, experimental GPF ash loading results are presented. Since most of the ash accumulated in the filter results from the combustion of lubricating oil additives, a burner test bench with a purpose-designed oil injection system was chosen for the investigations. The analysis of the backpressure results show that, contrary to high soot loadings, the ash load has a relatively low impact on engine performance and fuel consumption.
Technical Paper

Assessment of Different Included Spray Cone Angles and Injection Strategies for PCCI Diesel Engine Combustion

For compliance with legislative regulations as well as restricted resources of fossil fuel, it is essential to further reduce engine-out emissions and increase engine efficiency. As a result of lower peak temperatures and increased homogeneity, premixed Low-Temperature Combustion (LTC) has the potential to simultaneously reduce nitrogen oxides (BSNOx) and soot. However, LTC can lead to higher emissions of unburnt total hydrocarbons (BSTHC) and carbon monoxide (BSCO). Furthermore, losses in efficiency are often observed, due to early combustion phasing (CA50) before top dead center (bTDC). Various studies have shown possibilities to counteract these drawbacks, such as split-injection strategies or different nozzle geometries. In this work, the combination of both is investigated. Three different nozzle geometries with included spray angles of 100°, 120°, and 148° and four injection strategies are applied to investigate the engine performance.
Journal Article

Assessment of the Full Thermodynamic Potential of C8-Oxygenates for Clean Diesel Combustion

Within the Cluster of Excellence “Tailor-Made Fuels from Biomass” (TMFB) at the RWTH Aachen University, two novel biogenic fuels, namely 1-octanol and its isomer dibutyl ether (DBE), were identified and extensively analyzed in respect of their suitability for combustion in a Diesel engine. Both biofuels feature very different properties, especially regarding their ignitability. In previous works of the research cluster, promising synthesis routes with excellent yields for both fuels were found, using lignocellulosic biomass as source material. Both fuels were investigated as pure components in optical and thermodynamic single cylinder engines (SCE). For 1-octanol at lower part load, almost no soot emission could be measured, while with DBE the soot emissions were only about a quarter of that with conventional Diesel fuel. At high part load (2400 min-1, 14.8 bar IMEP), the soot reduction of 1-octanol was more than 50% and for DBE more than 80 % respectively.
Journal Article

Characterization of Hollow Cone Gas Jets in the Context of Direct Gas Injection in Internal Combustion Engines

Direct injection (DI) compressed natural gas (CNG) engines are emerging as a promising technology for highly efficient and low-emission engines. However, the design of DI systems for compressible gas is challenging due to supersonic flows and the occurrence of shocks. An outwardly opening poppet-type valve design is widely used for DI-CNG. The formation of a hollow cone gas jet resulting from this configuration, its subsequent collapse, and mixing is challenging to characterize using experimental methods. Therefore, numerical simulations can be helpful to understand the process and later to develop models for engine simulations. In this article, the results of high-fidelity large-eddy simulation (LES) of a stand-alone injector are discussed to understand the evolution of the hollow cone gas jet better.
Journal Article

Crank-Angle Resolved Real-Time Engine Modelling: A Seamless Transfer from Concept Design to HiL Testing

Virtual system integration and testing using hardware-in-the-loop (HiL) simulation enables front-loading of development tasks, provides a safer and reliable testing environment and reduces prototype hardware costs. One of the greatest challenges to overcome when performing HiL simulations is assuring a high model accuracy under stringent real-time requirements with acceptable development effort. This article represents a novel solution by deriving the plant model for HiL directly from the existing detailed models from the component layout phase using co-simulation methodology. It provides an effective and efficient model implementation and validation process followed by detailed quantitative analysis of the test results referred to the engine test bench measurements.
Journal Article

Development and Demonstration of LNT+SCR System for Passenger Car Diesel Applications

The regulations for mobile applications will become stricter in Euro 6 and further emission levels and require the use of active aftertreatment methods for NOX and particulate matter. SCR and LNT have been both used commercially for mobile NOX removal. An alternative system is based on the combination of these two technologies. Developments of catalysts and whole systems as well as final vehicle demonstrations are discussed in this study. The small and full-size catalyst development experiments resulted in PtRh/LNT with optimized noble metal loadings and Cu-SCR catalyst having a high durability and ammonia adsorption capacity. For this study, an aftertreatment system consisting of LNT plus exhaust bypass, passive SCR and engine independent reductant supply by on-board exhaust fuel reforming was developed and investigated. The concept definition considers NOX conversion, CO2 drawback and system complexity.
Journal Article

Effects of Cavitation and Hydraulic Flip in 3-Hole GDI Injectors

The performance of Gasoline Direct Injection (GDI) engines is governed by multiple physical processes such as the internal nozzle flow and the mixing of the liquid stream with the gaseous ambient environment. A detailed knowledge of these processes even for complex injectors is very important for improving the design and performance of combustion engines all the way to pollutant formation and emissions. However, many processes are still not completely understood, which is partly caused by their restricted experimental accessibility. Thus, high-fidelity simulations can be helpful to obtain further understanding of GDI injectors. In this work, advanced simulation and experimental methods are combined in order to study the spray characteristics of two different 3-hole GDI injectors.
Technical Paper

Experimental Investigation of the Effect of Multiple Injections on Pollutant Formation in a Common-Rail DI Diesel Engine

In Common-Rail DI Diesel Engines, multiple injection strategies are considered as one of the methodologies to achieve optimum performance and emission reduction. However, multiple injections open a whole new horizon of parameters which affect the combustion process. These parameters include the number of injection events, the duration between the starts of each injection event, the splitting of the total fuel mass on the different injection events, etc. In the present work, the influence of the number of injection events and the influence of the duration between the starts of each injection event on emission levels are investigated. Combustion and pollutant formation were experimentally investigated in a Common-Rail DI Diesel engine. The engine was operated at conventional part-load conditions with 2000 rpm, no external EGR, and an injected fuel mass of 15 mg/cycle.
Technical Paper

Experimental Investigation of the Spray Characteristics of Di-n-Butyl Ether (DNBE) as an Oxygenated Compound in Diesel Fuel

Increasing concern for the environment and the impending scarcity of fossil fuels requires continued development in hydrocarbon combustion science. For compression-ignition engines, adding oxygenated compounds to the fuel can reduce noise, soot formation, and unburned hydrocarbons while simultaneously increasing thermal efficiency. In order to reliably model and design compression-ignition engines to use new fuel blends, accurate spray characteristic data is required. In this study, the spray characteristics of various blends of the oxygenated compound di-n-butyl ether (DNBE) with standard EN590 Diesel fuel are presented, including spray cone angle and spray penetration length for both liquid and gas phases. The experiments were conducted in a spray chamber at ambient conditions of 50 bar and 800 K, simulating TDC conditions in a Diesel engine. Injection pressures were varied from 700-1600 bar.
Technical Paper

In-Use Compliance Opportunity for Diesel Powertrains

In-use compliance under LEV III emission standards, GHG, and fuel economy targets beyond 2025 poses a great opportunity for all ICE-based propulsion systems, especially for light-duty diesel powertrain and aftertreatment enhancement. Though diesel powertrains feature excellent fuel-efficiency, robust and complete emissions controls covering any possible operational profiles and duty cycles has always been a challenge. Significant dependency on aftertreatment calibration and configuration has become a norm. With the onset of hybridization and downsizing, small steps of improvement in system stability have shown a promising avenue for enhancing fuel economy while continuously improving emissions robustness. In this paper, a study of current key technologies and associated emissions robustness will be discussed followed by engine and aftertreatment performance target derivations for LEV III compliant powertrains.
Technical Paper

Increasing Efficiency in Gasoline Powertrains with a Two-Stage Variable Compression Ratio (VCR) System

Downsizing in combination with turbocharging currently represents the main technology trend for meeting CO2 emissions with gasoline engines. Besides the well-known advantages of downsizing the compression ratio has to be reduced in order to mitigate knock at higher engine loads along with increased turbocharging demand to compensate for the reduction in power. Another disadvantage occurs at part load with increasing boost pressure levels causing the part load efficiencies to deteriorate. The application of a variable compression ratio (VCR) system can help to mitigate these disadvantages. The 2-stage VCR system with variable kinetic lengths entails variable powertrain components which can be used instead of the conventional components and thus only require minor modifications for existing engine architectures. The presented variable length connecting rod system has been continuously developed over the past years.
Technical Paper

Influence of Vehicle Operators and Fuel Grades on Particulate Emissions of an SI Engine in Dynamic Cycles

With the implementation of the “Worldwide harmonized Light duty Test Procedure” (WLTP) and the highly dynamic “Real Driving Emissions” (RDE) tests in Europe, different engineering methodologies from virtual calibration approaches to Engine-in-the-loop (EiL) methods have to be considered to define and calibrate efficient exhaust gas aftertreatment technologies without the availability of prototype vehicles in early project phases. Since different types of testing facilities can be used, the effects of test benches as well as real and virtual vehicle operators have to be determined. Moreover, in order to effectively reduce harmful emissions, the reproducibility of test cycles is essential for an accurate and efficient application of exhaust gas aftertreatment systems and the calibration of internal combustion engines.
Technical Paper

Influence of the Nozzle Spray Angle on Pollutant Formation and Combustion Efficiency for a PCCI Diesel Engine

In Common-Rail DI Diesel Engines, a low combustion temperature process is considered as one of the most important possibilities to achieve very small emissions and optimum performance. To reduce NOx and Soot strongly, it is necessary to achieve a homogenization of the mixture in order to avoid the higher local temperatures which are responsible for the NOx formation [1]. Through the homogenization it is also possible to obtain a stoichiometric air-fuel ratio in order to significantly reduce the Soot emissions. One way to achieve this homogeneous condition is to start injection very early together with the use of higher EGR rates. The direct effect of these conditions cause a longer ignition delay (this is the time between start of the injection and auto-ignition during physical and chemical sub processes such as fuel atomization, evaporation, fuel air mixing and chemical pre-reactions take place) so that the mixture formation has more time to achieve a homogeneous state.
Technical Paper

Injection Rate Shaping Investigations on a Small – Bore DI Diesel Engine

So far, the effect of injection rate shaping on the diesel combustion in small-bore DI diesel engines has not been extensively investigated, especially at high part load conditions with high EGR rates. The benefit of injection rate shaping is already verified for heavy duty engines at high load conditions with and without EGR. For this investigation, single cylinder engine investigations were conducted at the VKA / RWTH Aachen University. In order to meet the future NOx legislation limits like US-Tier2Bin5 it is crucial to reduce NOx especially at the high load points of the certification cycles, as FTP75 or US06. For the single cylinder investigations two part load points were chosen, which have relevance for the mentioned certification cycles. The experimental work focuses on different rate shapes as rectangular (Common-Rail type), ramp and boot shape at high EGR rates.
Journal Article

Laser-Induced Incandescence Measurements of Tailor-Made Fuels in an Optical Single-Cylinder Diesel Engine

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.
Technical Paper

Lower Emissions in Commercial Diesel Engines through Waste Heat Recovery

In order to comply with demanding Greenhous Gas (GHG) standards, future automotive engines employ advanced engine technologies including waste heat recovery (WHR) systems. A waste heat recovery system converts part of engine wasted exergies to useful work which can be fed back to the engine. Utilizing this additional output power leads to lower specific fuel consumption and CO2 emission when the total output power equals the original engine output power. Engine calibration strategies for reductions in specific fuel consumption typically results in a natural increase of NOx emissions. The utilization of waste heat recovery systems provides a pathway which gives both reduction in emissions and reduction in specific fuel consumption. According to DOE (Department of Energy), US heavy-duty truck engines’ technology need to be upgraded towards higher brake thermal efficiencies (BTE). DOE target is BTE>55% for Class-8 heavy-duty vehicles in the United States.
Journal Article

Numerical Investigation of Direct Gas Injection in an Optical Internal Combustion Engine

Direct injection (DI) of compressed natural gas (CNG) is a promising technology to increase the indicated thermal efficiency of internal combustion engines (ICE) while reducing exhaust emissions and using a relatively low-cost fuel. However, design and analysis of DI-CNG engines are challenging because supersonic gas jet emerging from the DI injector results in a very complex in-cylinder flow field containing shocks and discontinuities affecting the fuel-air mixing. In this article, numerical simulations are used supported by validation to investigate the direct gas injection and its influence on the flow field and mixing in an optically accessible ICE. The simulation approach involves computation of the in-nozzle flow with highly accurate Large-Eddy Simulations, which are then used to obtain a mapped boundary condition. The boundary condition is applied in Unsteady Reynolds Averaged Navier-Stokes simulations of the engine to investigate the in-cylinder velocity and mixing fields.
Technical Paper

Objectified Drivability Evaluation and Classification of Passenger Vehicles in Automated Longitudinal Vehicle Drive Maneuvers with Engine Load Changes

To achieve global market and brand specific drivability characteristics as unique selling proposition for the increasing number of passenger car derivatives, an objectified evaluation approach for the drivability capabilities of the various cars is required. Thereto, it is necessary to evaluate the influence of different engine concepts in various complex and interlinked powertrain topologies during engine load change maneuvers based on physical criteria. Such an objectification approach enables frontloading of drivability related engineering tasks by the execution of drivability development and calibration work within vehicle subcomponent-specific closed-loop real-time co-simulation environments in early phases of a vehicle development program. So far, drivability functionalities could be developed and calibrated only towards the end of a vehicle development program, when test vehicles with a sufficient level of product maturity became available.
Technical Paper

Optical Investigation of Biofuel Effects on NO and PAH Formation in Diesel-Like Jets

In order to reduce engine out CO2 emissions it is a main subject to find new alternative fuels out of renewable sources. For this reason in this paper a blend out of 1-octanol and di-n-butylether and pure di-n-butylether are investigated in comparison to n-heptane as diesel-like fuel. The alternative fuels have a different combustion behavior particularly concerning important combustion parameters like ignition delay and mixture formation. Especially the formation of pollutants like nitrogen oxides in the combustion of alternative fuels is of global interest. The knowledge of the combustion behavior is important to design new engine geometries or implement a new calibration of the engine. In previous measurements in a single cylinder engine it was found out that both alternative fuels form nearly no soot emissions. For this reason now NOx is investigated optically to avoid the traditional soot NOx trade-off in diesel combustion.