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Renewable fuels, such as bio- and e-fuels, are of great interest for the defossilization of the transport sector. Among these fuels, methanol represents a promising candidate for emission reduction and efficiency increase due to its very high knock resistance and its production pathway as e-fuel. In general, reliable simulation tools are mandatory for evaluating a specific fuel potential and optimizing combustion systems. In this work, a previously presented methodology (Esposito et al., Energies, 2020) has been refined and applied to a different engine and different fuels. Experimental data measured with a single cylinder engine (SCE) are used to validate RANS 3D-CFD simulations of gaseous engine-out emissions. The RANS 3D-CFD model has been used for operation with a toluene reference fuel (TRF) gasoline surrogate and methanol. Varying operating conditions with exhaust gas recirculation (EGR) and air dilution are considered for the two fuels.

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. Especially for coated GPF applications, the prognosis of the emission conversion performance over lifetime poses an ambitious challenge, which significantly influences future catalyst diagnosis calibrations. The paper presents key-findings for the different GPF application variants. In the first part, experimental GPF ash loading results are presented. Ash accumulates as thin wall layers and short plugs, but does not penetrate into the wall. However, it suppresses deep bed filtration of soot, initially decreasing the soot-loaded backpressure. For the emission calibration, the non-linear backpressure development complicates the soot load monitoring, eventually leading to compromises between high safety against soot overloading and a low number of active regenerations.

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.

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.

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.

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.

One of the main challenges in internal combustion engine design is the simultaneous reduction of all engine pollutants like carbon monoxide (CO), total unburned hydrocarbons (THC), nitrogen oxides (NOx), and soot. Low-temperature combustion (LTC) concepts for compression ignition (CI) engines, e.g., premixed charged compression ignition (PCCI), make use of pre-injections to create a partially homogenous mixture and achieve an emission reduction. However, they present challenges in the combustion control, with the usage of in-cylinder pressure sensors as feedback signal is insufficient to control heat release and pollutant emissions simultaneously. Thus, an additional sensor, such as an ion-current sensor, could provide further information on the combustion process and effectively enable clean and efficient PCCI operation.

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.

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.

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.

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.

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.

Although spark-ignited engines have a considerable development history, the relevant flow physics and geometry design implications are still not fully understood. One reason is the lack of experimental and numerical methods with sufficiently high resolution or capabilities of capturing stochastic phenomena which could be used as part of the development cycle. More recently, Large-Eddy simulation (LES) has been identified as a promising technique to establish a better understanding of in-cylinder flow variations. However, simulations of engine configurations are challenging due to resolution as well as modeling requirements and computational cost for these unsteady multi-physics problems. LES on full engine geometries can even be prohibitively expensive. For this reason, the size of the computational LES domain is here reduced to the region of physical interest and boundary conditions are obtained from a RANS simulation of the whole experimental flow domain.

In the last years the research activities in the field of lightweighting have been advancing rapidly. The introduction of innovative materials and manufacturing technologies has allowed significant weight reduction. Despite this, novel technologies and materials have not reached a wide distribution. The reasons for this are mainly high production costs and environmental impacts of manufacturing that do not compensate benefits during operation. The paper deals with the AffordabLe LIghtweight Automobiles AlliaNCE (ALLIANCE) project which has the goal of developing novel advanced automotive materials and production technologies, aiming at an average 25% weight reduction over 100 k units/year, at costs of <3 €/kg. The article is focussed on Work Package 1 (WP1) of the project, aimed at estimating the full attributes of innovative design solutions by assessing costs, energy demand and GWP over the entire vehicle Life Cycle (LC).

Premixed charged compression ignition (PCCI) is an advanced combustion strategy, which has the potential to achieve ultra-low nitrogen oxide and soot emissions at high thermal efficiencies. PCCI combustion is characterized by a complex nonlinear chemical-physical process, which indicates that a physical description involves significant development times and also high computation cost. This paper presents a method to use cylinder pressure data and engine operations parameters for prediction of PCCI engine emissions by unsupervised learning and nonlinear identification techniques. The proposed method first uses principal component analysis (PCA) to reduce the dimension of the cylinder-pressure data. Based on the PCA analysis, a multi-input multi-out model was developed for nitrogen oxide and soot emission prediction by multi-layer perceptron (MLP) neural network.

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.

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.

Future Diesel engines must meet extended requirements regarding air-fuel ratio, exhaust gas recirculation (EGR) capability, and tailored exhaust gas temperatures in the complete engine map to comply with the future pollutant emission standards. In this respect, parallel turbines combined with two separate exhaust manifolds have the potential to increase the exhaust gas temperature upstream of the exhaust aftertreatment system and reduce the catalyst light-off time. Furthermore, variable exhaust valve (EV) lifts enable new control strategies of the boosting system without additional actuators. Therefore, hardware robustness can be improved. This article focuses on the parallel-sequential boosting concept (PSBC) for a high-performance four-cylinder Diesel engine with separated exhaust manifolds combined with EV deactivation. One EV per cylinder is connected to one of the separated exhaust manifolds and, thus, connected to one of the turbines.

Exhaust aftertreatment systems must function sufficiently over the full useful life of a vehicle. In Europe this is currently defined as 160.000 km. With the introduction of Euro 7 it is expected that the required mileage will be extended to 240.000 km. This will then be consistent with the US legislation. In order to quantify the emission impact of exhaust system degradation, an Euro 7 exhaust aftertreatment system is aged by different accelerated approaches: application of the Standard Bench Cycle, the ZDAKW cycle, a novel ash loading method and borderline aging. The results depict the impact of oil ash on the oxygen storage capacity. For tailpipe emissions, the maximum peak temperatures are the dominant aging factor. The cold start performance is effected by both, thermal degradation and ash accumulation. An evaluation of this emission increase requires appropriate benchmarks.

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.