High-speed characterization of ECN spray: a using various diagnostic techniques

Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called “Spray A”, has been defined with detailed ambient and injector conditions. For this paper, we describe results from the constant-volume pre-burn vessel at Eindhoven University of Technology. The executed measurements include a wide range of diagnostics to characterize “spray A” in reacting and non-reacting conditions in great detail. Observations of spray penetration, ignition, liquid length and flame lift-off location by using several high-speed imaging diagnostics are discussed and compared with other ECN participating institutes. Comparison Spray A data from the other participating institutes, as it was presented during the 2nd ECN workshop is gathered from the ECN website database. It can be concluded that the obtained results from the standardized ECN spray diagnostics, show satisfactory similarity, despite of the challenge to reach similar boundary conditions (ambient and injector) in each of the unique facilities. The differences in results are within the measurement deviation and uncertainty or can be explained by the usage of (slightly) different injectors. Combining the results of the different measurement techniques provides an overall (time resolved) overview where the different phases of fuel injection are directly linked and summarized. The presented overview provides a direct input for (CFD) modeling validation

A numerical study of a premixed flame on a slit burner

A numerical study of a premixed methane/air flame on a 4 mm slit burner is presented. A local grid refinement technique is used to deal with large gradients and curvature of all variables encountered in the flame, keeping the number of grid points within reasonable bounds. The method used here leads to a large reduction in the number of mesh points, compared to global or line-by-line refinement techniques. The procedure to obtain the initial guess for the detailed model simulation, needed for the Newton-like solution method, is discussed. The method uses the result of a one-step global model simulation of the same geometry and an appropriate one-dimensional detailed model simulation. The method works fine for the computations presented here. The results of the detailed model are compared to those of the one-step global reaction model computation. Furthermore, using a direct photograph of the luminescence, the flame-tip height and the general flame shape of the detailed simulation are verified with the corresponding experimental flame. Although only a qualitative comparison can be made, both the height and the flame shape compare well

Comparative study on the effects of inlet heating, inlet boosting, and double-injection strategy on partially premixed combustion

\u3cp\u3e Partially premixed combustion (PPC) is a low temperature combustion (LTC) concept which can relieve soot-NO \u3csub\u3ex\u3c/sub\u3e trade-off without sacrificing efficiency. However, at low load operating range, PPC with low reactivity fuel generally undergoes long ignition delay, which gives rise to high pressure rise rate, fast heat release and even misfires. To solve these problems and maintain high efficiency simultaneously, inlet heating, inlet boosting and double-injection strategy are experimentally investigated in a heavy-duty engine. BH80 (80vol% n-butanol and 20vol% n-heptane) are blended and tested at 8 bar gIMEP in PPC mode. Inlet heating (from 40 \u3csup\u3eo\u3c/sup\u3e C to 100 \u3csup\u3eo\u3c/sup\u3e C), inlet boosting (from 1.4 bar to 2.5 bar) and a double-injection strategy (pilot/main injection) are attempted to reduce the maximum pressure rise rate (PRRmax). The results show that all three methods can achieve negligible soot emissions. Moreover, a correlation between global temperature at TDC and ignition delay is noticed. In other words, high global temperature after compression stroke makes BH80 easier to ignite. As a consequence, the ignition delay shortens and the maximum pressure rise rate decreases. Compared to inlet heating and inlet boosting, the double-injection strategy shows more advantages in reducing pressure rise rates and obtaining high gross indicated efficiency (GIE). Specifically, with a well-tuned double-injection strategy, 3.6 bar/ \u3csup\u3eo\u3c/sup\u3e CA PRRmax and 49.5% GIE are achieved. In addition, when more fuel is injected in the pilot injection pulse, NO \u3csub\u3ex\u3c/sub\u3e emissions are significantly decreased. However, a longer pilot pulse also produces more CO and HC emissions and leads to lower combustion efficiency. \u3c/p\u3

Performance and emission studies in a heavy-duty diesel engine fueled with an N-butanol and N-heptane blend

\u3cp\u3eN-butanol, as a biomass-based renewable fuel, has many superior fuel properties. It has a higher energy content and cetane number than its alcohol competitors, methanol and ethanol. Previous studies have proved that n-butanol has the capability to achieve lower emissions without sacrifice on thermal efficiency when blended with diesel. However, most studies on n-butanol are limited to low blending ratios, which restricts the improvement of emissions. In this paper, 80% by volume of n-butanol was blended with 20% by volume of n-heptane (namely BH80). The influences of various engine parameters (combustion phasing, EGR ratio, injection timing and intake pressure, respectively) on its combustion and emission characteristics are tested at different loads. The results showed that when BH80 uses more than 40% EGR, the emitted soot and nitrogen oxides (NOx) emissions are below the EURO VI legislation. Carbon monoxide (CO) decreases and NOx emissions increase with the increase of injection pressure. It was also found that for a constant lambda (1.55) the stable operating load range of BH80 is limited to relatively high load (>8 bar gross indicated mean effective pressure (IMEPg)). However, higher boost conditions can help to reduce its maximum pressure rise rate and achieve stable combustion at 8 bar IMEPg.\u3c/p\u3

Effects of different injection strategies and EGR on partially premixed combustion

\u3cp\u3ePremixed Charge Compression Ignition concepts are promising to reduce NOx and soot simultaneously and keeping a high thermal efficiency. Partially premixed combustion is a single fuel variant of this new combustion concepts applying a fuel with a low cetane number to achieve the necessary long ignition delay. In this study, multiple injection strategies are studied in the partially premixed combustion approach to reach stable combustion and ultra-low NOx and soot emission at 15.5 bar gross indicated mean effective pressure. Three different injection strategies (single injection, pilot-main injection, main-post injection) are experimentally investigated on a heavy duty compression ignition engine. A fuel blend (70 vol% n-butanol and 30 vol% n-heptane) was tested. The effects of different pilot and post-injection timing, as well as Exhaust-gas Recirculation rate on different injection strategies investigated. All the measurements were performed at the same load, combustion phasing, lambda and engine speed. The results show that all three injection strategies produced ultra-low soot emission, while less NOx emission was noticed for pilot-main injection because of less diffusion combustion mode. Pilot-main injection strategy decreases the maximum pressure rise rate effectively compared to single injection. For pilot-main injection at 15.5 bar gross indicated mean effective pressure, when 24.3% (pilot/total fuel mass ratio) of fuel injected at -30 crank angle after top dead center in the pilot and the rest injected in the main with 45% EGR rate, 48.97% gross indicated efficiency is achieved. In addition, ultra-low soot (0.19 ppm) and NOx (0.327 g/kWh) emissions are achieved respectively without using after treatment.\u3c/p\u3

Large eddy simulation of n-dodecane spray flames using flamelet generated manifolds

\u3cp\u3eIn the present study the Engine Combustion Network (ECN) Spray A target conditions are investigated using the Large Eddy Simulation (LES) and the Flamelet Generated Manifold (FGM) methods. We investigate n-dodecane spray flames at three different ambient oxygen levels in engine relevant conditions. The flamelet database is generated by simulating the counterflow diffusion flamelets for two recently developed n-dodecane mechanisms with 257-species/1521-reactions (Narayanaswamy et al., 2014) and 130-species/2395-reactions (Ranzi et al., 2014). In addition to validation in non-reacting conditions, we evaluate the performance of the newly implemented FGM model by comparing spray ignition delay times and flame lift-off lengths to the available experimental data within the ECN. The obtained ignition delay times agree well with the experimental data for the mechanism by Ranzi et al., 2014 and are over-predicted for the mechanism by Narayanaswamy et al., 2014. This observation is consistent with a respective trend in the observed flame lift-off lengths. Further, we provide evidence of only minor spray realization to realization variation of the ignition delay time in the present configuration. The spray flame structure is noted to consist of two parts: (1) a diffusion flame enveloping the combusting part of the spray close to the stoichiometric isoline, and (2) a premixed combustion regime in the fuel-rich core of the spray. During spray ignition, the model predicts the spatio-temporal phases of ignition. The model also indicates the presence of a 'cool flame' between the flame lift-off length and the nozzle. For the first time, we quantify the size of such a topological structure. In general, the flamelet data showed significant differences in the ignition characteristics between the two chemical mechanisms for all three ambient oxygen cases, but indicated little differences for a steady flame.\u3c/p\u3

Effects of EGR at various loads on diesel engine performance and exhaust particle size distribution using four blends of RON70 and diesel

Partially premixed combustion (PPC) is an efficient way to produce low oxides of nitrogen (NOx) and soot emissions simultaneously at low and medium loads, and the combustion phasing can be controlled through the change of injection event. Previous studies demonstrate that PPC applying regular diesel fuel can be achieved with a low compression ratio (CR) diesel engine using more than 70% exhaust gas recirculation (EGR) at 8 bar indicated mean effective pressure (IMEP). While diesel PPC has a combustion efficiency lower than 90% due to the lower CR and excessive EGR conditions. If we want to get PPC on a higher CR engine using reasonable EGR rate and with a moderate injection advance, the easiest approach is to use fuels having higher octane number or equivalently lower cetane number. The combustion and emission characteristics of four blends with research octane number (RON) 70 are experimentally investigated at various loads with a sweep of EGR rates and compared to that of conventional combustion with regular diesel. The first blend is a primary reference fuel with a RON of 70, denoted as PRF. The other three blends are n-heptane/iso-octane blended with ethanol or n-butanol or toluene separately to obtain RON 70 as well, they are denoted as ERF, BRF and TRF. Tests are performed on a heavy duty diesel engine with a CR of 15.7 applying a single injection strategy in this study. The results indicate that the four blends are dominated by premixed combustion at low and medium loads and produce low NOx and soot emissions simultaneously. At high load, a large amount of fuel needs to be injected into the cylinder hence the relatively long injection duration prevents to have a separation between fuel injection event and combustion event. Then the convention diesel combustion has be used to ensure high fuel economy. Compared with other fuels, ERF and BRF yield considerably less particulate matter emissions resulting from their favourable equivalence ratios due to their oxygen content and higher volatility. The particle size distribution curves for all the test fuels in general shift towards bigger size as engine load is increased. Results also show that when more EGR rate is used the number concentration of nucleation-mode particles reduces and more accumulation-mode particles are generated. Effects of EGR at various loads on diesel engine performance and exhaust particle size distribution using four blends of RON70 and diesel. Available from: https://www.researchgate.net/publication/309391432_Effects_of_EGR_at_various_loads_on_diesel_engine_performance_and_exhaust_particle_size_distribution_using_four_blends_of_RON70_and_diesel [accessed Aug 2, 2017]

Heat2Control:modeling of Split-injection Spray-A Case from ECN with FGM in OpenFOAM

Diesel like combustion is mostly preferred for the internal combustion engines due to its efficiency. However, it has several drawbacks at which emissions are one of them. Reducing emissions down while keeping the efficiency high is a tough task to cope with. In this respect, multi-phase injection studies are performed in order to control the combustion since diesel combustion is mostly a mixing controlled process. In this project, nominal condition for the double injection Spray-A case from Engine Combustion Network (ECN) is modelled with Flamelet-Generated-Manifold (FGM) in OpenFOAM computational fluid dynamics (CFD) tool with Reynolds Averaged Navier-Stokes (RANS) turbulence model to validate the solver code that will be used for engine applications later on. FGM is an efficient chemistry reduction method, which holds good accuracy while keeping the computational power lower compared to the other reduction methods for chemical kinetics. The solver code for OpenFOAM is from Lib-ICE library (Lucchini, 2013). FGM method is implemented into the OpenFOAM solver since the original solver utilizes Tabulation of Dynamic Adaptive Chemistry (TDAC) method for chemical kinetics. TDAC solves transport equations for chemical kinetics online; therefore it’s limited to chemical reaction mechanisms with 50-species and 100-reactions whilst FGM method is suitable for larger reaction mechanisms since the chemistry is decoupled from the flow field. FGM look-up table stores sources terms for transport equations and thermophysical variables that are required for transport equations with respect to user-defined controlling variables. Besides, selected species can be stored in the look-up table to be retrieved with respect to the controlling variables. Furthermore, thermophysical properties are updated with the virtual-fuel approach. In this respect, a linear system is solved to evaluate virtual species mass fractions by satisfying the conservation of energy, mixture properties, and elemental masses. This approach improves the computational time significantly, 30 times faster for each CFD simulation of 3 [ms], compared to the original OpenFOAM solver code with TDAC and provides comparable results. the chemistry effects on ignition and lift-off length for both injections that are computed in CFD simulations with respect to the different chemical reaction mechanism, which are for n-dodecane surrogate fuel. The smallest mechanism (Yao, 2015) in terms of the number of species gives comparable results for ignition delays and lift-off lengths with respect to the experimental results, (Skeen, 2015)

Modelling of common rail fuel injection system and influence of fluid properties on injection process

This paper focuses on the modelling of a research type Heavy Duty Common Rail (CR) fuel injection system. More specifically it reports on the observed interaction between fuel properties and injection and on the capability to model this. For that reason a hydraulic model of the fuel injection system has been developed using the AMESim code (Imagine S.A., 2003). The reliability of the numerical results is tested through a comparison between numerical and experimental results when using regular diesel fuel. Basis for this detailed comparison are measurements of injected mass flow rate, needle lift and pressure oscillations in the injection duct for a single injection. Simulation results for regular diesel show good agreement with measured data for pressure oscillations in the injection duct, needle lift and injected fuel mass flow rate. A comparison of experimental and simulated results for Rapeseed oil Methyl Ester (RME) also shows good correspondence, which proves the capability of the model to capture the influence of different fuel properties