Multidimensional Modeling of Diesel Ignition and Combustion Using a Multistep Kinetics Model

Ignition and combustion mechanisms in diesel engines were studied using the KIVA code, with modifications to the combustion, heat transfer, crevice flow, and spray models. A laminar-and-turbulent characteristic-time combustion model that has been used successfully for spark-ignited engine studies was extended to allow predictions of ignition and combustion in diesel engines. A more accurate prediction of ignition delay was achieved by using a multistep chemical kinetics model. The Shell knock model was implemented for this purpose and was found to be capable of predicting successfully the autoignition of homogeneous mixtures in a rapid compression machine and diesel spray ignition under engine conditions. The physical significance of the model parameters is discussed and the sensitivity of results to the model constants is assessed. The ignition kinetics model was also applied to simulate the ignition process in a Cummins diesel engine. The post-ignition combustion was simulated using both a single-step Arrhenius kinetics model and also the characteristic-time model to account for the energy release during the mixing-controlled combustion phase. The present model differs from that used in earlier multidimensional computations of diesel ignition in that it also includes state-of-the-art turbulence and spray atomization models. In addition, in this study the model predictions are compared to engine data. It is found that good levels of agreement with the experimental data are obtained using the multistep chemical kinetics model for diesel ignition modeling. However, further study is needed of the effects of turbulent mixing on post-ignition combustion.

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Comparing Single-Step and Multi-Step Chemistry Using The Laminar and Turbulent Characteristic Time Combustion Model In Two Diesel Engines

10.4271/2002-01-1749 ◽

2002 ◽

Cited By ~ 4

Author(s):

Ossi Kaario ◽

Martti Larmi ◽

Franz Tanner

Keyword(s):

Diesel Engines ◽

Characteristic Time ◽

Single Step ◽

Combustion Model ◽

Turbulent Characteristic

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A Study on Biodiesel NOx Emission Control With the Reduced Chemical Kinetics Model

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4027358 ◽

2014 ◽

Vol 136 (10) ◽

Cited By ~ 1

Author(s):

Juncheng Li ◽

Zhiyu Han ◽

Cai Shen ◽

Chia-fon Lee

Keyword(s):

Chemical Kinetics ◽

Combustion Process ◽

Operating Conditions ◽

Nox Emission ◽

Kinetics Model ◽

Combustion Model ◽

Nox Emissions ◽

Soot Emission ◽

Start Of Injection ◽

Combustion Processes

In this paper, the effects of the start of injection (SOI) timing and exhaust gas recirculation (EGR) rate on the nitrogen oxides (NOx) emissions of a biodiesel-powered diesel engine are studied with computational fluid dynamics (CFD) coupling with a chemical kinetics model. The KIVA code coupling with a CHEMKIN-II chemistry solver is applied to the simulation of the in-cylinder combustion process. A surrogate biodiesel mechanism consisting of two fuel components is employed as the combustion model of soybean biodiesel. The in-cylinder combustion processes of the cases with four injection timings and three EGR rates are simulated. The simulation results show that the calculated NOx emissions of the cases with default EGR rate are reduced by 20.3% and 32.9% when the injection timings are delayed by 2- and 4-deg crank angle, respectively. The calculated NOx emissions of the cases with 24.0% and 28.0% EGR are reduced by 38.4% and 62.8%, respectively, compared to that of the case with default SOI and 19.2% EGR. But higher EGR rate deteriorates the soot emission. When EGR rate is 28.0% and SOI is advanced by 2 deg, the NOx emission is reduced by 55.1% and soot emission is controlled as that of the case with 24% EGR and default SOI. The NOx emissions of biodiesel combustion can be effectively improved by SOI retardation or increasing EGR rate. Under the studied engine operating conditions, introducing more 4.8% EGR into the intake air with unchanged SOI is more effective for NOx emission controlling than that of 4-deg SOI retardation with default EGR rate.

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Modeling HPDI Natural Gas Heavy Duty Engine Combustion

ASME 2005 Internal Combustion Engine Division Fall Technical Conference (ICEF2005) ◽

10.1115/icef2005-1307 ◽

2005 ◽

Cited By ~ 4

Author(s):

Guowei Li ◽

Tim Lennox ◽

Dale Goudie ◽

Mark Dunn

Keyword(s):

Natural Gas ◽

Test Data ◽

Direct Injection ◽

Cfd Modeling ◽

Combustion Model ◽

Model Parameters ◽

Prediction Errors ◽

Engine Test ◽

Gas Ignition ◽

Ignition And Combustion

CFD Modeling of the injection, the mixing, the combustion and the emission formation processes in a high pressure direct injection (HPDI) natural gas engine is presented in this paper. KIVA3V was used together with an injector model. Two sub-models had been developed that the concurrent injection, ignition and combustion of natural gas and diesel could be simulated. The gas injection was simulated with the injector model. In the injector model, the electromagnetism, the hydraulics and the mechanics were computed by solving a set of ordinary differential equations. Based on the engine experimental data, a combustion model was built in which premixed combustion of natural gas was excluded and the natural gas ignition was initiated by the pilot diesel combustion rather than a spontaneous process. The model calibration and validation are discussed. The model parameters were tuned against one set of engine test data. For the model validation, 30 engine test data were applied. The data were from HPDI engine tests at varied engine speeds, loads and injection timings with and without EGR. The model gave good agreement with the engine tests having no EGR. However, the model, in general, under-predicted the burning rate. With EGR, the model prediction errors were large and the NOx were under-predicted, though the trends were still captured.

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Further Developments on a Characteristic Time Model for NOx Emissions from Diesel Engines

10.4271/982460 ◽

1998 ◽

Cited By ~ 16

Author(s):

K. P. Duffy ◽

A. M. Mellor

Keyword(s):

Diesel Engines ◽

Characteristic Time ◽

Nox Emissions ◽

Time Model

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A Study on Biodiesel NOx Emission Control With the Reduced Chemical Kinetics Model

Volume 2: Fuels; Numerical Simulation; Engine Design, Lubrication, and Applications ◽

10.1115/icef2013-19205 ◽

2013 ◽

Author(s):

Juncheng Li ◽

Chia-fon F. Lee ◽

Zhiyu Han ◽

Cai Shen ◽

Mianzhi Wang

Keyword(s):

Chemical Kinetics ◽

Nox Emission ◽

Kinetics Model ◽

Combustion Model ◽

Nox Emissions ◽

Soot Emission ◽

Start Of Injection ◽

Soybean Biodiesel ◽

Combustion Processes ◽

Gas Recirculation

In this paper, the effects of the start of injection (SOI) timing and EGR rate on the nitrogen oxide (NOx) emissions of biodiesel-powered diesel engine are studied with computational fluid dynamics (CFD) coupling with a chemical kinetics model. A surrogate biodiesel mechanism consisting of two fuel components is employed as the combustion model of soybean biodiesel. The in-cylinder combustion processes of the cases with four injection timings and three exhaust gas recirculation (EGR) rates are simulated. The simulation results show that the NOx emissions of biodiesel combustion can be effectively improved by SOI retardation or increasing EGR rate. The calculated NOx emissions of the cases with default EGR rate are reduced by 20.3% and 32.9% when the injection timings are delayed by 2-degree and 4-degree crank angle, respectively. The calculated NOx emissions of the cases with 24.0% and 28.0% EGR are reduced by 38.4% and 62.8%, respectively, compared to that of the case with default SOI and 19.2% EGR. But higher EGR rate deteriorates the soot emission. When EGR rate is 28.0% and SOI is advanced by 2-degree, the NOx emission is reduced by 55.1% and soot emission is controlled as that of the case with 24% EGR and default SOI.

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Interpreting airborne pandemics spreading using fractal kinetics’ principles

F1000Research ◽

10.12688/f1000research.53196.1 ◽

2021 ◽

Vol 10 ◽

pp. 609

Author(s):

Panos Macheras ◽

Athanasios A. Tsekouras ◽

Pavlos Chryssafidis

Keyword(s):

Preventive Measures ◽

Herd Immunity ◽

Real Life ◽

Kinetics Model ◽

Mixed System ◽

Model Parameters ◽

Population Mobility ◽

Fractal Kinetics ◽

Time Model ◽

The Impact

Introduction The reaction between susceptible and infected subjects has been studied under the well-mixed hypothesis for almost a century. Here, we present a consistent analysis for a not well-mixed system using fractal kinetics’ principles. Methods We analyzed COVID-19 data to get insights on the disease spreading in absence/presence of preventive measures. We derived a three-parameter model and show that the “fractal” exponent h of time larger than unity can capture the impact of preventive measures affecting population mobility. Results The h=1 case, which is a power of time model, accurately describes the situation without such measures in line with a herd immunity policy. The pandemic spread in four model countries (France, Greece, Italy and Spain) for the first 10 months has gone through four stages: stages 1 and 3 with limited to no measures, stages 2 and 4 with varying lockdown conditions. For each stage and country two or three model parameters have been determined using appropriate fitting procedures. The fractal kinetics model was found to be more akin to real life. Conclusion Model predictions and their implications lead to the conclusion that the fractal kinetics model can be used as a prototype for the analysis of all contagious airborne pandemics.

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