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Ultrafine particles, in particular solid sub-100 nm particles pose high risks to human health due to their high lung deposition efficiency, translocation to all organs including the brain and their harmful chemical composition; due to dense traffic, the population in urban environments is exposed to high concentrations of those toxic air contaminants, despite these facts, they are still widely neglected. Therefore, the EU-Commission set up a program for clean and competitive solutions for different problem areas which are regarded to be hotspots of such particles. HORIZON AeroSolfd is an EU project, co-funded by Switzerland that will deliver affordable, adaptable, and sustainable retrofit solutions to reduce exhaust tailpipe emissions from petrol engines, brake emissions and pollution in semi-closed environments.

Optical soot pyrometry is a mature experimental technique that has been applied to a broad range of combustion systems for measuring soot temperature and concentration. Even though the method is widely used and well documented, the line of sight nature of the technique makes the interpretation of its results challenging. Notably, gradients in temperature and soot concentration along the line of sight or across the field of view can introduce significant levels of uncertainty in the results. This paper presents a numerical study where the signal from the experimental two-color pyrometry technique in a marine diesel engine reference experiment is reconstructed employing computational fluid dynamics (CFD) and a detailed Line-by-Line (LBL) spectral radiation model. The analysis is aimed at qualitatively supporting interpretability of experimental observations.

Butanol, a four-carbon alcohol, is considered in the last years as an interesting alternative fuel, both for Diesel and for gasoline application. Its advantages for engine operation are: good miscibility with gasoline and diesel fuels, higher calorific value than ethanol, lower hygroscopicity, lower corrosivity and possibility of replacing aviation fuels. Like ethanol, butanol can be produced as a biomass-based renewable fuel or from fossil sources. In the research project, DiBut (Diesel and butanol) addition of butanol to Diesel fuel was investigated from the points of view of engine combustion and of influences on exhaust aftertreatment systems and emissions. One investigated engine (E1) was with emission class “EU Stage 3A” for construction machines, another one, engine (E2) was HD Euro VI. The most important findings are: with higher butanol content, there is a lower heat value of the fuel and there is lower torque at full load.

State of the art high-pressure fuel injectors offer the ability to inject multiple times per cycle, and can reach very low fuel amounts per injection event. This behaviour allows the application of pilot injections in diesel engine applications or dual fuel engines. In both diesel and dual fuel engines, the amount of pilot fuel affects the engine efficiency. The understanding of the underlying ignition mechanism of the pilot fuel is required to optimize injection parameters and the engines’ fuel consumption. The present work focuses on the differences of ignition mechanisms between long and short injections. The investigation has been performed numerically, using CFD with a well-proven combustion model. The setup used employs a well characterized single orifice injector, injecting into a high temperature, pressurized environment with a composition of 15% oxygen.

An independent periodical technical inspection (PTI)*) of vehicles is proposed in the last time as a better prevention against increased emissions of the fleet. Several projects focused on the Diesel vehicles (HD & LD) and on the functionality of the exhaust aftertreatment systems as a key element for lowering emissions of a vehicle or machine. The present paper summarizes the results obtained on 3 modern passenger cars Euro 6b (with EGR, DOC, DPF & SCR) during load jumps, representing the heat-up or cool-down behaviour of the exhaust system. The portable devices for PTI were tested together with the stationary measuring systems of the engine laboratory. In the second part of the report, the present knowledge and proposals of supplementary test procedures (like IUC or PTI) were shortly described.

In this study, a novel 3D-CFD combustion model employing Flamelet Generated Manifolds (FGM) for dual fuel combustion was developed. Validation of the platform was carried out using recent experimental results from an optically accessible Rapid Compression Expansion Machine (RCEM). Methane and n-dodecane were used as model fuels to remove any uncertainties in terms of fuel composition. The model used a tabulated chemistry approach employing a reaction mechanism of 130 species and 2399 reactions and was able to capture non-premixed auto ignition of the pilot fuel as well as premixed flame propagation of the background mixture. The CFD model was found to predict well all phases of the dual fuel combustion process: I) the pilot fuel ignition delay, II) the Heat Release Rate of the partially premixed conversion of the micro pilot spray with entrained methane/air and III) the sustained background mixture combustion following the consumption of the spray plume.

It is well-known that the spatial distribution of turbulence intensity and fuel concentration at spark-time play a pivotal role on the flame development within the pre-chamber in gas engines equipped with a scavenged pre-chamber. The combustion within the pre-chamber is in turn a determining factor in terms of combustion behaviour in the main chamber, and accordingly it influences the engine efficiency as well as pollutant emissions such as NOx and unburned hydrocarbons. This paper presents a numerical analysis of fuel concentration and turbulence distribution at spark time for an automotive-sized scavenged pre-chamber mounted at the head of a rapid compression-expansion machine (RCEM). Two different pre-chamber orifice orientations are considered: straight and tilted nozzles. The latter introduce a swirling flow within the pre-chamber. Simulations have been carried out using with two different turbulence models: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES).

In the general efforts to replace the fossil fuels in transportation by renewable fuels the bioalcohols are an important alternative. The global share of Bioethanol used for transportation is continuously increasing. Butanol, a four-carbon alcohol, is considered in the last years as an interesting alternative fuel, both for Diesel and for Gasoline application. Its advantages for engine operation are: good miscibility with gasoline and diesel fuels, higher calorific value than Ethanol, lower hygroscopicity, lower corrosivity and possibility of replacing aviation fuels. In the present work research with different nButanol portions in gasoline (BuXX)* was performed on the 2-cylinder SI engine with variations of several parameters on engine dynamometer. At different steady state operating points were varied: spark timing (αz), air excess factor (λ) and EGR-rate. Furthermore, the conversion rates and light-off of a 3-way-catalyst were investigated.

Dual-fuel natural gas engines are seen as an attractive solution for simultaneous reduction of pollutant and CO2 emissions while maintaining high engine thermal efficiency. However, engines of this type exhibit a tradeoff between misfire as well as high UHC emissions for small pilot injection amounts and higher emissions of soot and NOX for operation strategies with higher pilot fuel proportion. The aim of this study was to investigate POMDME as an alternative pilot fuel having the potential to mitigate the emissions tradeoff, enabling smokeless combustion due to high degree of oxygenation, and being less prone to misfire due to its higher cetane number. Furthermore, POMDME can be synthetized carbon neutrally. First, characteristics of POMDME ignition in methane/air mixture and the transition into premixed flame propagation were investigated optically in a rapid compression-expansion machine (RCEM) by employing Schlieren and OH* chemiluminescence imaging.

The sooting propensity of dual-fuel combustion with n-dodecane pilot injection in a lean-premixed methane-air charge has been investigated using an optically accessible Rapid Compression-Expansion Machine (RCEM) to achieve engine-relevant pressure and temperature conditions at the start of pilot injection. A Diesel injector with a 100 μm single-hole coaxial nozzle, mounted at the cylinder periphery, has been employed to admit the pilot fuel. The aim of this study was to enhance the fundamental understanding of soot formation and oxidation processes of n-dodecane in the presence of methane in the air charge by parametric variation of methane equivalence ratio, charge temperature, and pilot fuel injection duration. The influence of methane on ignition delay and flame extent of the pilot fuel jet has been determined by simultaneous excited-state hydroxyl radical (OH*) chemiluminescence and Schlieren imaging.

Further efforts to reduce the air pollution from traffic are undertaken worldwide and the filtration of exhaust gas will also be increasingly applied on gasoline cars (GPF1 … gasoline particle filter). In the present paper, some results of investigations of nanoparticles from four MPI gasoline cars are represented. The measurements were performed at vehicle tailpipe and in CVS-tunnel. Moreover, two variants of GPF were investigated on a high-emitting modern vehicle, including analytics of PAH and attempts of soot loading in road application. The modern MPI vehicles can emit a considerable amount of PN, which in some cases attains the level of Diesel exhaust gas without DPF and can pass over the actual European limit value for GDI (6.0 x 1011 #/km). The GPF-technology offers in this respect further poten-tials to reduce the PN-emissions of traffic.

In the present work numerical simulations were carried out investigating the effect of fuel type, nozzle-geometry variations and back-pressure changes on high-pressure gas injections under application-relevant conditions. Methane, hydrogen and nitrogen with a total pressure of 500 bar served as high-pressure fuels and were injected into air at rest at 200 bar and 100 bar. Different nozzle shapes were simulated and the analysis of the results lead to a recommendation for the most advantageous geometry regarding jet penetration, volumetric growth, mixing enhancement and discharge coefficient. Additionally an artificial inlet boundary conditions was tested for the use with real-gas thermodynamics and was shown to be capable of reducing the simulation time significantly.

Formation of soot in an auto-igniting n-dodecane spray under diesel engine relevant conditions has been investigated numerically. As opposed to research addressing turbulence-chemistry interaction (TCI) by coupling diffusive turbulence models with more sophisticated models in the context of Reynolds-Averaged Navier-Stokes equations (RANS), this study employs the advanced sub-grid scale k-equation model in the framework of a Large Eddy Simulation (LES) together with the uninvolved Direct Integration (DI) approach. A reduced n-heptane chemical mechanism has been employed and artificially accelerated in order to predict the ignition for n-dodecane accurately. Soot processes have been modelled with an extended version of the semi-empirical, two-equation model of Leung, which considers C2H2 as the soot precursor and accounts for particle inception, surface growth by C2H2 addition, oxidation by O2, oxidation by OH and particle coagulation.

The interaction of turbulent premixed methane combustion with the surrounding flow field can be studied using optically accessible test rigs such as a rapid compression expansion machine (RCEM). The high flexibility offered by such a test rig allows its operation at various thermochemical conditions at ignition. However, limitations inherent to such test rigs due to the absence of an intake stroke do not allow turbulence production as found in IC-engines. Hence, means to introduce turbulence need to be implemented and the relevant turbulence quantities have to be identified in order to enable comparability with engine relevant conditions. A dedicated high-pressure direct injection of air at the beginning of the compression phase is considered as a measure to generate adjustable turbulence intensities at spark timing and during the early flame propagation.

Large-bore natural gas engines may use pre-chamber ignition. Despite extensive research in engine environments, the exact nature of the jet, as it exits the pre-chamber orifice, is not thoroughly understood and this leads to uncertainty in the design of such systems. In this work, a specially-designed rig comprising a quartz pre-chamber fit with an orifice and a turbulent flowing mixture outside the pre-chamber was used to study the pre-chamber flame, the jet, and the subsequent premixed flame initiation mechanism by OH* and CH* chemiluminescence. Ethylene and methane were used. The experimental results are supplemented by LES and 0D modelling, providing insights into the mass flow rate evolution at the orifice and into the nature of the fluid there. Both LES and experiment suggest that for large orifice diameters, the flow that exits the orifice is composed of a column of hot products surrounded by an annulus of unburnt pre-chamber fluid.

Cycle-to-cycle variations in internal combustion engines are known to lead to limitations in engine load and efficiency, as well as increases in emissions. Recent research has led to the identification of the source of cyclic variations of pressure, soot and NO emissions in direct injection common rail diesel engines, when employing a single block injection and operating under long ignition delay conditions. The variations in peak pressure arise from changes in the diffusion combustion rate, caused by randomly occurring in-cylinder pressure fluctuations. These fluctuations result from the excitation of the first radial mode of vibration of the cylinder gases which arises from the rapid premixed combustion after the long ignition delay period. Cycles with high-intensity fluctuations present faster diffusion combustion, resulting in higher cycle peak pressure, as well as higher measured exhaust NO concentrations.

The operation of dual fuel engines, operated with natural gas as main fuel, offers the potential of substantial savings in CO2. Nevertheless, the operating map area where low pollutant emissions are produced is very narrow. Especially at low load, the raw exhaust gas contains high concentrations of unburned methane and, with high pilot fuel portions due to ignition limitations, also soot. The analysis of the combustion in those conditions in particular is not trivial, since multiple combustion modes are present concurrently. The present work focuses on the evaluation of the individual combustion modes of a dual fuel engine, operated with natural gas as main and diesel as pilot fuel, using a combustion model. The combustion has been split in two partwise concurrent combustion phases: the auto-ignition phase and the premixed flame propagation phase.

In this study, the combustion of butanol, neat and mixed with gasoline, was investigated on a 0.6 liter two-cylinder spark ignition engine with fully adjustable fuel injection and spark timing, coupled with an eddy current dynamometer. Two isomers of butanol, n-butanol and iso-butanol, were examined. This basic parameter study gives information about potential requirements of engine control systems for butanol FFV. Compared to the traditionally used ethanol, butanol does not exhibit hygroscopic behaviour, is chemically less aggressive and has higher energy density. On other hand, different laminar burning velocity and higher boiling temperature of butanol, compared to gasoline, requires some countermeasures to keep the engine operation reliable and efficient.

In the present paper some results of investigations of nanoparticles from five DI gasoline cars are represented. The measurements were performed at vehicle tailpipe and in CVS-tunnel. Moreover, five variants of “vehicle - GPF” were investigated. These results originate from the project GasOMeP (Gasoline Organic & Metal Particulates), which focused on metal-nanoparticles (including sub 20nm) from gasoline cars with different engine technologies. The PN-emission level of the investigated GDI cars in WLTC without GPF is in the same range of magnitude very near to the actual limit value of 6.0 × 1012 #/km. With the GPF’s with better filtration quality, it is possible to lower the emissions below the future limit value of 6.0 × 1011 #/km. There is no visible nuclei mode and the ultrafine particle concentrations below 10mm are insignificant. Some of the vehicles show at constant speed operation a periodical fluctuation of the NP-emissions, as an effect of the electronic control.

This study investigates n-dodecane split injections of “Spray A” from the Engine Combustion Network (ECN) using two different turbulence treatments (RANS and LES) in conjunction with a Conditional Moment Closure combustion model (CMC). The two modeling approaches are first assessed in terms of vapor spray penetration evolutions of non-reacting split injections showing a clearly superior performance of the LES compared to RANS: while the former successfully reproduces the experimental results for both first and second injection events, the slipstream effect in the wake of the first injection jet is not accurately captured by RANS leading to an over-predicted spray tip penetration of the second pulse. In a second step, two reactive operating conditions with the same ambient density were investigated, namely one at a diesel-like condition (900K, 60bar) and one at a lower temperature (750K, 50bar).