Numerical Evaluation of a New Strategy of Emissions Reduction by Urea Direct Injection for Heavy Duty Diesel Engines

The effect of ammoniac deoxidizing agent (Urea) on the reduction of NOx produced in the Diesel engine was investigated numerically. Urea dissolved in water was directly injected into the engine cylinder during the expansion stroke. The NOx deoxidizing process was described using a simplified chemical kinetic model coupled with the comprehensive kinetics of Diesel oil surrogate combustion. If the technology of DWI (Direct Water Injection) with the later injection timing was used, the deoxidizing reactants could be delivered in a controlled amount directly into the flame plume zones, where NOx formed. Numerical simulations for the Isotta Fraschini DI Diesel engine were carried out using the KIVA-3V code, modified to account for the “co-fuel” injection and reaction with combustion products. The results showed that the amount of NOx could be substantially reduced up to 80% with the injection timing and the fraction of Urea in the solution optimized

CFD-3D Analysis of a Light Duty Dual Fuel (Diesel/Natural Gas) Combustion Engine

AbstractNowadays, the most critical issues concerning internal combustion engines are the reduction of the pollutant emissions, in particular of CO2, and the replacement of fossil fuels with renewable sources. An interesting proposition for Diesel engines is the Dual Fuel (DF) combustion, consisting in the ignition of a premixed charge of gaseous fuel (typically natural gas) by means of a pilot injection of Diesel Fuel.Dual fuel combustion is a quite complex process to model, since it includes the injection of liquid fuel, superimposed with a premixed combustion. However, CFD simulation is fundamental to address a number of practical issues, such as the setting of the liquid injection parameters and of the gaseous fuel metering, as well as to get the maximum benefit from the DF technique.In this paper, a customized version of the KIVA-3V Computational Fluid Dynamic (CFD) code was adopted to analyze the combustion process of a 4-cylinder, 2.8 l, turbocharged HSDI Diesel engine, operating in both Diesel and DF (Diesel and Natural Gas) modes.Starting from a previously validated diesel combustion model, a natural gas combustion model was implemented and added to simulate the DF operations. Available engine test data were used for validation of the diesel-only operation regimes. Using the calibrated model, the influence of the premixed charge composition was investigated, along with the effect of the diesel injection advance angle, at a few characteristic operating conditions. An optimum setting was eventually found, allowing the DF engine to deliver the same brake power of the original Diesel unit, yielding the same maximum in-cylinder pressure.It was found that DF combustion is soot-less, yields a strong reduction of CO and CO2, but also an increase of NO

Experimental and numerical investigation of split injections at low load in an hddi diesel engine equipped with a piezo injector

In order to investigate the effects of split injection on emission formation and engine performance,experiments was carried out using a heavy duty single cylinder Diesel engine. Split injections with varied dwell Time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the parameters selected to investigate,other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezoelectric injector. To interpret the observed phenomena,engine CFD simulations using the KIVA-3V code were also made. The results show that a reduction in NOx emissions and brake specific fuel consumption was achieved for short dwell times whereas they were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of sinGle injections. The results indicated,however,no increase in soot as a result of splitting the injection in two parts. Both HC and CO emissions were found to increase with split injections.In order to investigate the effects of split injection on emission formation and engine performance, experiments were carried out using a heavy duty single cylinder diesel engine. Split injections with varied dwell time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the selected parameters, other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezo-electric injector. To interpret the observed phenomena, engine CFD simulations using the KIVA-3V code were also made. The results show that reductions in NOx emissions and brake specific fuel consumption were achieved for short dwell times whereas they both were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of single injections. The results indicated, however, no increase in soot as a result of splitting the injection in two parts. Both HC and CO emissions were found to increase with split injections. Copyright © 2006 SAE International

Development of a Direct Evaporator for the Organic Rankine Cycle

This paper describes research and development currently underway to place the evaporator of an Organic Rankine Cycle (ORC) system directly in the path of a hot exhaust stream produced by a gas turbine engine. The main goal of this research effort is to improve cycle efficiency and cost by eliminating the usual secondary heat transfer loop. The project’s technical objective is to eliminate the pumps, heat exchangers and all other added cost and complexity of the secondary loop by developing an evaporator that resides in the waste heat stream, yet virtually eliminates the risk of a working fluid leakage into the gaseous exhaust stream. The research team comprised of Idaho National Laboratory and General Electric Company engineers leverages previous research in advanced ORC technology to develop a new direct evaporator design that will reduce the ORC system cost by up to 15%, enabling the rapid adoption of ORCs for waste heat recovery

CFD modeling of emissions formation and reduction in heavy duty diesel engines

Bu çalışmada, özellikle ağır vasıta dizel motorunda azot oksit (NOx) ve is (C(s)) emisyonlarının oluşumu ve azaltılması, Sayısal Akışkanlar Dinamiği (CFD) modellemesi yardımıyla incelenmektedir. KIVA-3VR2 ve CHEMKIN-II paketi modelleme için kullanılmıştır. Chalmers University of Technology’de geliştirilen n-heptan ve toluen karışımından oluşan dizel yakıt modeli (Disesel Oil Surrogate, DOS), türbülans/yanma etkileşimin içini kısmi karışımlı reaktör modeli (Partially Stirred Reactor, PaSR), detaylı reaksiyon mekanizması ve geliştirilmiş demet modeli KIVA-3VR2'ye uyarlanmış ve modellemeler gerçekleştirilmiştir. Dizel yakıt modeli ve reaksiyon mekanizması sabit hacimli bomba deneylerinde, değişik basınç ve hava fazlalık katsayısı (HFK, l), değerleri için, sıcaklığa bağlı tutuşma gecikmesi (TG) esas alınarak doğrulanmıştır. Sonraki aşamada Volvo D12C ağır vasıta dizel motorunda 18.5 ve 14.0 sıkıştırma oranları, farklı yük, püskürtme zamanı değerleri ve egzoz gazı geri dönüşü (EGR) oranları için modelleme çalışmaları yapılarak deney verileri ile karşılaştırılmıştır. Elde edilen sonuçlara göre, silindir içi basınç ve sıcaklık değerleri, ısı açığa çıkış hızı ve yanma verimi deney sonuçlarıyla uyumludur. NOx ve is emisyonları eğilim olarak deney sonuçlarıyla uyumludur ancak nicel olarak geliştirmeye ihtiyaç vardır. Emisyonlardaki farklılığın nedeni olarak, modelleme için kullanılan detaylı reaksiyon mekanizmasındaki is yanması, NOx ve CO oluşum reaksiyonları arasındaki çok hassas ve birbirini etkileyen dengenin henüz tam olarak sağlanamamış olması gösterilebilir. Bu konuda geliştirmeye ihtiyaç duyulmaktadır. Anahtar Kelimeler: Dizel motoru, modelleme, NOx-is emisyonları.  The main emission problem for conventional diesel combustion is NOx-soot tradeoff (diesel dilemma) which could not be completely eliminated with the in-cylinder combustion techniques till now and still after-treatment process is necessary to meet the present emission legislations. Also with the development of the new engines which have different combustion regimes such as Homogeneous Charge Compression Ignition (HCCI), Modulated Kinetics (MK), Low Temperature Combustion (LTC), Premixed Charge Compression Ignition (PCCI), new emissions such as HC and CO became significant for compression ignition engines. This study mainly investigates formation and reduction of NOx and soot emissions in diesel engine combustion, especially in Heavy Duty Diesel (HDD) engines with the help of CFD engine modeling. KIVA-3VR2 and CHEMKIN-II package were used for the modeling purposes. CHALMERS' Diesel Oil Surrogate (DOS) model based on a blend of aliphatic (n-heptane, 70%) and aromatic (toluene, 30%) components, turbulence/chemistry interaction approach with Partially Stirred Reactor (PaSR) model, detailed chemical mechanism and modified spray model were implemented into the KIVA-3VR2 code for the modeling tasks. DOS and detailed chemical mechanism were validated comparing the ignition delay (ID) times with the present available shock tube data for different temperatures at different pressure and excess air ratios, l. Validation of the DOS and its constituents shows that developed reaction mechanism represents well enough ID and Negative Temperature Dependence behavior. Also it is calculated that for different l values (1 / Equivalence Ratios, ER) ignition delay time reduces with the increasing of ER (e.g., for rich mixtures) which is consistent with the experiments. Then modeling results for Volvo D12C engine at MK combustion (Compression Ratio, CR, 18.0) and LTC (CR = 14.0) regimes were compared with the experimental data. Present reaction mechanism is modified in order to improve its NOx-soot emissions behavior which has a good emission calculation tendency, but still quantitatively weak. Different fuel injection times, loads and both EGR-free and EGR cases were studied to extend the modeling capability. The MK combustion regimes in the Volvo D12C DI diesel engine realized under selected retarded fuel injections (e.g. Start of Injection, SOI, varied from -5 till to 10 Crank Angle Degree (CAD) After Top Dead Centre (ATDC) causing the ID to be longer than the injection duration. For injection timings, -5, 0, 5 and 10 ATDC, predicted trends clearly indicate that the combustion mode shifts from conventional diesel-like to HCCI-like mode following from early to late injection cases. This behavior is not clear in the pressure vs. crank angle curves because these retarded injections corresponds to the expansion part of the cycle, and expansion avoids sudden pressure rise sourced from HCCI-like combustion. However it is clearly visible from the Rate of Heat Release (RoHR) curves that, in retarded injection conditions, RoHR maxima increase as expected because of the increased premixed combustion phase, which increases ID times in such a way that ignition occurs after the completion of fuel injection process similar to the HCCI combustion mode. For all cases, calculation results for in-cylinder pressure, temperature, RoHR and combustion efficiency are in a good agreement with experimental results. NOx and soot emissions are reasonably well also. Although tendency of the calculated emissions is good, a quantitative improvement for emission predictions, especially for soot emissions, is required. In diesel combustion, most of the combustion process takes place over soot-formation and soot-oxidation path and soot emission is the difference between these formed and oxidized soot amount, which corresponds to only a small fraction of formed soot ( =1%). Hence modeling of soot emissions is very hard, e.g., even 1% calculation error for soot oxidation will drastically affect the resulted soot emissions. NOx formation is also strictly coupled with the soot-oxidation process because the remained oxygen radical which is necessary for NO formation depends on the soot-oxidation process. If soot-oxidation part is dominant in the mechanism, then excessive soot oxidation process can result lower soot emissions than the real amount by consuming most of the available oxygen radical which will be used later for the NO formation reactions. In conclusion excessive soot oxidation gives less soot emissions and indirectly prevents proper amount of NO formation. For this reason more accurate modeling of NOx-soot emissions in the presented detailed chemistry approach requires a proper balance between soot-oxidation and NO, CO formation reactions. Keywords: Diesel combustion, NOx-soot emissions, CFD modeling.

Numerical Evaluation of a New Strategy of Emission reduction by EREA Direct Injection for Heavy Duty Diesel Engines

The effect of ammoniac deoxidizing agent (Urea) on the reduction of NOx produced in the Diesel Engine was invesrigated numerically. The results showed that the amount of NOx could be substantially reduced up to 80% with the Urea injection timing and its fraction in the solution optimized

CFD Modeling of Diesel Oil and DME Performance in a Two-Stroke Free Piston Engine

The paper presents the CFD model and numerical results of combustion process simulations in a two-stroke, uniflow scavenging dual free piston engine, FPE, designed for electricity generation. Two fuels, diesel oil and dimethyl ether (DME),were studied in order to achieve HCCI-like combustion. It is illustrated that by varying the direc injection timing, a conparably efficient, low emission operation has been predicted for both fuel

CFD Modeling of Diesel Oil and DME Performance in a Two-Stroke Free Piston Engine

The paper presents the CFD model and numerical results of combustion process simulations in a two-stroke, uniflow scavenging dual free piston engine, FPE, designed for electricity generation. Two fuels, diesel oil and dimethyl ether (DME),were studied in order to achieve HCCI-like combustion. It is illustrated that by varying the direc injection timing, a conparably efficient, low emission operation has been predicted for both fuel

Injection Strategy Optimization for a Light Duty DI Diesel Engine in Medium Load Conditions with High EGR rates

Further restrictions on NOx emissions and theexpansion of current driving cycles for passenger caremission regulations to higher load operation in thenear future (such as the US06 supplement to theFTP-75 driving cycle) requires attention to lowemission combustion concepts in medium to highload regimes.One possibility to reduce NOx emissions is to increasethe EGR rate. The combustion-temperature reducingeffects of high EGR rates can significantly reduce NOformation, to the point where engine-out NOxemissions approach zero levels. However, engine-outsoot emissions typically increase at high EGR levels,due to the reduced soot oxidation rates at reducedcombustion temperatures and oxygen concentrations.The work presented in this paper focuses on theoptimization of a triple injection strategy to study theeffect of injection timing, fuel mass distribution overthe different injections and fuel rail pressure onemissions, combustion noise and fuel consumptionfor operation at medium load (10 bar IMEP andupwards) and high EGR rates (41%). The results ofsome of the test cases are compared with thoseobtained from modelling in KIVA-3V.By using an optimized triple injection strategy, sootemission levels could be reduced to below 0.04g/kWh and NOx emissions to below 0.4 g/kWh at amedium engine load of 10 bar IMEP in a singlecylinder research engine