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Technical Paper

Analysis of Cyclic Fluctuations of Charge Motion and Mixture Formation in a DISI Engine in Stratified Operation

Engine processes are subject to cyclic fluctuations, which a have direct effect on the operating and emission behavior of the engine. The fluctuations in direct injection gasoline engines are induced and superimposed by the flow and the injection. In stratified operation they can cause serious operating problems, such as misfiring. The current state of knowledge on the formation and causes of cyclic fluctuations is rather limited, which can be attributed to the complex nature of flow instabilities. The current investigation analyzes the cyclic fluctuations of the in-cylinder charge motion and the mixture formation in a direct injection gasoline engine using laser-optical diagnostics and numerical 3D-calculation. Optical measurement techniques and pressure indication are used to measure flow, mixture formation, and combustion processes of the individual cycles.
Technical Paper

Cold Start Emission Reduction by Barrier Discharge

Dielectric barrier discharge (DBD) offers the advantage to excite and dissociate molecules in the exhaust gas stream. Those dissociated and excited species are oxidizing or reducing harmful exhaust gas components. The advantage of a plasma chemical system in comparison to a catalytic measure for exhaust gas treatment is the instantaneous activity at ambient temperature from the starting of the engine. The investigations reviewed in this paper are dealing with the plasma chemical oxidation of hydrocarbons in the exhaust gas stream during cold start conditions. The article concerns the design and development of a plasma-system in order to decrease the hydrocarbon emissions from engine start till catalyst light off. Vehicle results in the New European Driving Cycle show a hydrocarbon conversion of more than 42% in the first 11 seconds from engine start. In this period nearly all types of hydrocarbon were reduced.
Technical Paper

Experimental Investigation of the Origin of Cyclic Fluctuations in a DISI Engine by Means of Advanced Laser Induced Exciplex Fluorescence Measurements

Cyclic fluctuations of the in-cylinder processes in a Direct Injection Spark Ignition (DISI) engine may strongly affect the engine operation causing misfires or variations in the indicated mean effective pressure (imep). Particularly misfires prevent compliance with current or future exhaust emission legislations. Nevertheless, the origin of cyclic fluctuations is not well understood since fluctuations of in-cylinder air flow, fuel injection and wall interaction have to be considered. This paper focusses on a detailed experimental analysis of the origin of cyclic fluctuations in a DISI engine with an air guided combustion process by means of advanced Laser Induced Exciplex Fluorescence (LIEF) measurements. It reveals that cycle-to-cycle variations primarily originate from the air/fuel ratio at the spark plug.
Journal Article

Improving Engine Efficiency and Emission Reduction Potential of HVO by Fuel-Specific Engine Calibration in Modern Passenger Car Diesel Applications

The optimization study presented herein is aimed to minimize the fuel consumption and engine-out emissions using commercially available EN15940 compatible HVO (Hydrogenated Vegetable Oil) fuel. The investigations were carried out on FEV’s 3rd generation HECS (High Efficiency Combustion System) multi-cylinder engine (1.6L, 4 Cylinder, Euro 6). Using a global DOE approach, the effects of calibration parameters on efficiency and emissions were obtained and analyzed. This was followed by a global optimization procedure to obtain a dedicated calibration for HVO. The study was aiming for efficiency improvement and it was found that at lower loads, higher fractions of low pressure EGR in combination with lower fuel injection pressures were favorable. At higher loads, a combustion center advancement, increase of injection pressure and reduced pilot injection quantities were possible without exceeding the noise and NOx levels of the baseline Diesel.
Technical Paper

Investigation of Spray-Bowl Interaction Using Two-Part Analysis in a Direct-Injection Diesel Engine

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.
Technical Paper

Optical Spray Investigations on OME3-5 in a Constant Volume High Pressure Chamber

Synthetic fuels generated with surplus renewable electricity, water and captured CO2, so called E-fuels, offer the possibility to easily store excess energy over long periods of time. Therefore, the ALIGN-CCUS-project seeks to use them for power-generation and as a fuel for the transport-sector. Polyoxymethylene-dimethyl-ethers (POMDMEs, short: OME) are promising E-fuels for passenger-car applications. Their molecular structure is CH3-O-(CH2O)n-CH3. For passenger-car applications, OME-mixtures with n between 3 and 5 seem most suitable, as the mixture is liquid under normal ambient conditions, offers a high cetane-number and sufficient lubricity. Their high flash-point, low toxicity and good miscibility with conventional diesel-fuel also may ease their market-introduction.
Technical Paper

UV-Absorption Measurements by Spontaneous Raman Scattering in Low-Sooting Diesel-Like Jets

UV-absorption measurements are sparse in diesel(-like) combustion, particularly close to the premixed burn. Thus, such measurements are conducted in diesel-like jets in a high-pressure vessel in this work, using 1D spontaneous Raman scattering (SRS) from N2. Stokes (~263 nm) and anti-Stokes (~235 nm) SRS induced by a krypton fluoride excimer (KrF*) laser (~248 nm) is exploited. Anti-Stokes SRS can be directly used for attenuation correction of laser-induced fluorescence (LIF) from NO at ~236 nm. Results show the importance of attenuation correction, although the jets are largely non-sooting. To identify absorbers, effects of SRS wavelength, measurement time in the injection event, location in the flame, jet width (JW), temperature, CO concentration, and injection pressure are considered. Particularly strong attenuation observed around the time of second-stage ignition appears to be primarily caused by combustion intermediates such as partially oxidized fuel.