Computational fluid dynamics analysis of the effect of mixture heterogeneity on combustion process in a premixed charge compression ignition engine

2005 ◽  
Vol 6 (5) ◽  
pp. 487-495 ◽  
Author(s):  
K Saijyo ◽  
T Kojima ◽  
K Nishiwaki
Keyword(s):  
Mass Fraction ◽  
Initial Conditions ◽  
Combustion Process ◽  
Length Scale ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Heterogeneous Distribution ◽  
Fuel Mass ◽  
Computational Fluid Dynamics Analysis ◽  
Fuel Mass Fraction

We analyzed the interrelationships between mixture heterogeneity and reaction in a premixed charge compression ignition (PCCI) combustion, using large eddy simulation (LES) in conjunction with a reaction kinetics model. The aim of this analysis is to find the statistical characteristics of the mixture heterogeneity in a turbulent flowfield for moderating the PCCI combustion and for increasing an output limit, which is restricted by a severe knock. Several different initial conditions of heterogeneity of an air-fuel or air-fuel-EGR gas mixture were given at the intake valve closing time by a new method, which generated statistically reasonable turbulent fluctuations in both velocity and fuel mass fraction fields. The autoignition and combustion behaviours were analysed for several different sets of the r.m.s. and the length scale of the fluctuations in the fuel mass fraction. The analyses show that the combination of a larger r.m.s. value and a longer-length scale of the fluctuations in fuel mass fraction is effective to slow the combustion in a hot flame reaction phase and to avoid knocking. The analytical results also show that the heterogeneous distribution of an EGR gas has a considerable effect in making the combustion slower, even when a fuel-air mixture is homogeneous.

Availability analysis on combustion of n-heptane and isooctane blends in a reactivity controlled compression ignition engine

2017 ◽  
Vol 232 (11) ◽  
pp. 1501-1515 ◽  
Author(s):  
Mostafa Mohebbi ◽  
Masoud Reyhanian ◽  
Iraj Ghofrani ◽  
Azhar Abdul Aziz ◽  
Vahid Hosseini
Keyword(s):  
Heat Transfer ◽  
Mass Fraction ◽  
Fossil Fuels ◽  
Utilization Efficiency ◽  
Second Law ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Reactivity Controlled Compression Ignition ◽  
Fuel Mass ◽  
Availability Analysis

Unfortunately, energy demands and destruction of the environment from uncontrolled manipulation of fossil fuels have increased. Climate change concerns have resulted in the rapid use of new, alternative combustion technologies. In this study, reactivity controlled compression ignition (RCCI) combustion, which can simply be exploited in internal combustion (IC) engines, is investigated. To introduce and identify extra insightful information, an exergy-based study was conducted to classify various irreversibility and loss sources. Multidimensional models were combined with the primary kinetics mechanism to investigate RCCI combustion, incorporating the second law of thermodynamics. The n-heptane, a highly reactive fuel, was supplied by direct injection into the cylinder, whereas premixed fuel was supplied through the intake port in an isooctane/ n-heptane RCCI engine. For five n-heptane increments (5%, 7.5%, 15%, 25%, and 40%) and six different exhaust gas recirculation (EGR) rates (0%, 10%, 20%, 30%, 40%, and 50%), accumulation of different exergy terms was calculated. The results show that as EGR introduction increases from 0% to 50%, the exergy destruction increases from 21.1% to 28.9%. Furthermore, the value of exhaust thermomechanical exergy decreases from 18.4% to 14.4% of the mixture fuel chemical exergy. Among the five different high reactive fuel mass regimes, the 40% n-heptane mass fraction has the major heat transfer exergy owing to its advanced CA50 that exerts a unique influence on cylinder charge temperature of heat transfer layer. The utilization efficiency of exhaust in RCCI is less affected by the variation of reactive fuel mass fraction by contrast; it will significantly influence heat transfer availability. This study revealed that with increasing reactive fuel ( n-heptane) from 7.5% to 40% the irreversibility decreased from 28.6% to 25.8% and the second law efficiency first increased from 43.2% to 44.6% at 15% n-heptane then decreased to 42.9% at 40% n-heptane.

Reduction of NOx Emission of Heavy Duty Gas Turbines by Improving Mixing Quality Using CFD Tools

2003 ◽  
Author(s):  
Weiqun Geng ◽  
Douglas Pennell ◽  
Stefano Bernero ◽  
Peter Flohr
Keyword(s):  
Gas Turbines ◽  
Mass Fraction ◽  
Cross Flow ◽  
Nox Emission ◽  
Injection System ◽  
Water Tunnel ◽  
Injection Hole ◽  
Fuel Mass ◽  
Mixing Quality ◽  
Fuel Mass Fraction

Jets in cross flow are one of the fundamental issues for mixing studies. As a first step in this paper, a generic geometry of a jet in cross flow was simulated to validate the CFD (Computational Fluid Dynamics) tool. Instead of resolving the whole injection system, the effective cross-sectional area of the injection hole was modeled as an inlet surface directly. This significantly improved the agreement between the CFD and experimental results. In a second step, the calculated mixing in an ALSTOM EV burner is shown for varying injection hole patterns and momentum flux ratios of the jet. Evaluation of the mixing quality was facilitated by defining unmixedness as a global non-dimensional parameter. A comparison of ten cases was made at the burner exit and on the flame front. Measures increasing jet penetration improved the mixing. In the water tunnel the fuel mass fraction within the burner and in the combustor was measured across five axial planes using LIF (Laser Induced Fluorescence). The promising hole patterns chosen from the CFD computations also showed a better mixing in the water tunnel than the other. Distribution of fuel mass fraction and unmixedness were compared between the CFD and LIF results. A good agreement was achieved. In a final step the best configuration in terms of mixing was checked with combustion. In an atmospheric test rig measured NOx emissions confirmed the CFD prediction as well. The most promising case has about 40% less NOx emission than the base case.

Engine performance and emission characteristics of a compression ignition engine fuelled with diesel/dimethoxymethane blends

2005 ◽  
Vol 219 (7) ◽  
pp. 905-914 ◽  
Author(s):  
Y Ren ◽  
Z H Huang ◽  
D M Jiang ◽  
L X Liu ◽  
K Zeng ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Mass Fraction ◽  
Volume Fraction ◽  
Engine Performance ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Performance And Emission ◽  
Fuel Blends ◽  
Performance And Emissions ◽  
Combustion Phase

The performance and emissions of a compression ignition engine fuelled with diesel/dimethoxymethane (DMM) blends were studied. The results showed that the engine's thermal efficiency increased and the diesel equivalent brake specific fuel consumption (b.s.f.c.) decreased as the oxygen mass fraction (or DMM mass fraction) of the diesel/DMM blends increased. This change in the diesel/DMM blends was caused by an increased fraction of the premixed combustion phase, an oxygen enrichment, and an improvement in the diffusive combustion phase. A remarkable reduction in the exhaust CO and smoke can be achieved when operating on the diesel/DMM blend. Flat NO x/smoke and thermal efficiency/smoke curves are presented when operating on the diesel/DMM fuel blends, and a simultaneous reduction in both NO x and smoke can be realized at large DMM addition. Thermal efficiency and NO x give the highest value at 2 per cent oxygen mass fraction (or 5 per cent DMM volume fraction) for the combustion of diesel/DMM blends.

scholarly journals Research on combustion process of gasoline homogenous charge compression ignition engine

2018 ◽  
Vol 184 ◽  
pp. 01013
Author(s):  
Corneliu Cofaru ◽  
Mihaela Virginia Popescu
Keyword(s):  
Experimental Research ◽  
Fuel Injection ◽  
Combustion Process ◽  
Fuel Mixture ◽  
Spark Ignition Engine ◽  
Injection System ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Engine Operation ◽  
Homogenous Charge Compression Ignition

The paper presents the research designed to develop a HCCI (Homogenous Charge Compression Ignition) engine starting from a spark ignition engine platform. The chosen test engine was a single cylinder, four strokes provided with a carburettor. The results of experimental research data obtained on this version were used as a baseline for the next phase of the research. In order to obtain the HCCI configuration, the engine was modified, as follows: the compression ratio was increased from 9.7 to 11.5 to ensure that the air – fuel mixture auto-ignite and to improve the engine efficiency; the carburettor was replaced by a direct fuel injection system in order to control precisely the fuel mass per cycle taking into account the measured intake air-mass; the valves shape were modified to provide a safety engine operation by ensuring the provision of sufficient clearance beetween the valve and the piston; the exchange gas system was changed from fixed timing to variable valve timing to have the possibilities of modification of quantities of trapped burnt gases. The cylinder processes were simulated on virtual model. The experimental research works were focused on determining the parameters which control the combustion timing of HCCI engine to obtain the best energetic and ecologic parameters.

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