Optimization of Direct Water Injection Parameters to Improve the Trade-off Between Efficiency and NOx Emissions for a Lean-Burn CHP NG Engine

2020 ◽  
Author(s):  
Youssef Beltaifa ◽  
Sascha Holzberger ◽  
Ferhat Aslan ◽  
Maurice Kettner ◽  
Peter Eilts
Keyword(s):  
Pressure Difference ◽  
Water Injection ◽  
Injection Pressure ◽  
Nox Emissions ◽  
Exhaust Gas ◽  
Cfd Simulations ◽  
Lean Burn ◽  
Engine Efficiency ◽  
Direct Water Injection ◽  
Intake Stroke

Abstract In the medium and long term, cogeneration plants in Germany will play an important role in the transition towards a cleaner and more efficient electricity and heat generation, compared to the conventional uncoupled power plants. For most of the currently used CHP (Combined Heat and Power) units, which operate with a lean-burn process, the NOx emissions limit represents an obstacle to increasing the electrical efficiency. Therefore, the lean burn process has become less attractive because of stricter future NOx emissions limit. In this context, the stoichiometric combustion process with a three-way catalytic converter provides a solution. However, the present study shows that lean burn operation still has potential due to direct water injection into the combustion chamber. This work includes an experimental investigation of the impact of different injection parameters (beginning of injection timing, injection pressure difference and water-to-fuel ratio) on the effectiveness of direct water injection regarding the improvement of the trade-off between engine efficiency and NOx emissions. For the execution of the experimental investigations, a series-production CHP-engine was equipped with a direct injection system consisting of a high-pressure unit, a high-pressure pipe and a GDI-injector. For the injector integration, the cylinder head was machined sidewise (close to the exhaust gas valve). Furthermore, 3D CFD simulations of the injection process allowed gaining a deeper insight into the complex spray-flow interaction, wall film formation and evaporation at different injection timings. For the 3D CFD simulations, the spray model used was tuned with help of spray pictures, taken on the spray test bed. Water injection at the beginning of the intake stroke (330 °CA BFTDC) reduces NOx emissions most effectively. Moreover, it causes the least engine efficiency loss. The increase of the injection pressure difference (between 20 and 80 bar) leads to a significant increase of the engine efficiency. However, it has a secondary effect on the NOx emissions reduction. The lowest NOx emissions are reached with an injection pressure difference of 60 bar. The combination of direct water injection (at the beginning of the intake stroke, injection pressure difference of 60 bar) with earlier combustion phasings enables an increase in the engine efficiency and a simultaneous decrease in NOx emissions without loss in engine performance. Main drawbacks of water injection are longer combustion duration and higher CO and HC emissions. In addition, the lower exhaust gas temperature causes a deterioration of the conversion of the HC molecules in the oxidation catalyst and reduces the heat recovery efficiency of the CHP-system.

Effects of Ambient Air Humidity on Emissions and Efficiency of Large-Bore Lean-Burn Otto Gas Engines in Development and Application

2020 ◽  
Author(s):  
Tomas Bartkowski ◽  
Stefan Eicheldinger ◽  
Maximilian Prager ◽  
Georg Wachtmeister
Keyword(s):  
Air Conditioning ◽  
Test Bench ◽  
Water Injection ◽  
Measurement Data ◽  
Ambient Air ◽  
Injection System ◽  
Nox Emissions ◽  
Air Humidity ◽  
Ambient Conditions ◽  
Lean Burn

Abstract The use of large-bore Otto gas engines is currently spreading widely considering the growing share of Power-To-Gas (P2G) solutions using renewable energies. P2G with a Combined Heat and Power (CHP) plant offers a promising way of utilizing chemical energy storage to provide buffering for volatile energy sources such as wind and solar power all over the world. Therefore, ambient conditions like air temperature, humidity and pressure can differ greatly between the location and time of engine operation, influencing its performance. Especially lean-burn Otto processes are sensitive to changes in ambient conditions. Besides, targeted use of humidity variation (e.g. through water injection in the charge air or combustion chamber) can help to reduce NOx emissions at the cost of a slightly lower efficiency in gas engines, being an alternative to selective catalytic reduction (SCR) exhaust gas aftertreatment. The ambient air condition boundaries have to be considered already in the early stages of combustion development, as they can also have a significant effect on generated measurement data in combustion research. To investigate the behavior, a test bench with a natural gas (CNG) powered single-cylinder research engine (piston displacement 4.77 1) at the Institute of Internal Combustion Engines (LVK) of the Technical University of Munich (TUM) was equipped with a sophisticated charge air conditioning system. This includes an air compressor and refrigeration dryer, followed by temperature and pressure control, as well as a controlled injection system for saturated steam and homogenizing containers, enabling the test bench to precisely emulate a widespread area of charge air parameters in terms of pressure, temperature and humidity. With this setup, different engine tests were conducted, monitoring and evaluating the engine’s emission and efficiency behavior regarding charge air humidity. In a first approach, the engine was operated maintaining a steady air-fuel equivalence ratio λ, fuel energy input (Q̇fuel = const.) and center of combustion (MFB 50%) while the relative ambient humidity was varied in steps between 21% and 97% (at 22 °C and 1013.25 hPa). Results show a significant decrease in nitrogen oxides (NOx) emissions (−39.5%) and a slight decrease in indicated efficiency (−1,9%) while hydrocarbon (THC) emissions increased by around 60%. The generated data shows the high significance of considering charge air conditioning already in the development stage at the engine test bench. The comparability of measurement data depends greatly on ambient air humidity. In a second approach, the engine was operated at a constant load and constant NOx emissions, while again varying the charge air humidity. This situation rather reflects an actual engine behavior at a CHP plant, where today often NOx–driven engine control is used, maintaining constant NOx emissions. The decrease in indicated efficiency was comparable to the prior measurements, while the THC emissions showed only a mild increase (5%). From the generated data it is, for instance, possible to derive operational strategies to compensate for changes in ambient conditions while maintaining emission regulations as well as high-efficiency output. Furthermore, the results suggest possibilities, but also challenges of utilizing artificial humidification (e.g. through water injection) considering the effects on THC emissions and efficiency. A possible shift of the knocking limit to earlier centers of combustion with higher humidity is to be investigated. The main goal is the further decrease of NOx emissions, increase of efficiency, while still maintaining hydrocarbon emissions.

Gasoline engine performance simulation of water injection and low-pressure exhaust gas recirculation using tabulated chemistry

2020 ◽  
Vol 21 (10) ◽  
pp. 1857-1877 ◽  
Author(s):  
Tim Franken ◽  
Fabian Mauss ◽  
Lars Seidel ◽  
Maike Sophie Gern ◽  
Malte Kauf ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Nitrogen Oxide ◽  
Water Injection ◽  
Exhaust Gas Recirculation ◽  
Low Pressure ◽  
Exhaust Gas ◽  
Nitrogen Oxide Emissions ◽  
Direct Water Injection ◽  
Tabulated Chemistry ◽  
Gas Recirculation

This work presents the assessment of direct water injection in spark-ignition engines using single cylinder experiments and tabulated chemistry-based simulations. In addition, direct water injection is compared with cooled low-pressure exhaust gas recirculation at full load operation. The analysis of the two knock suppressing and exhaust gas cooling methods is performed using the quasi-dimensional stochastic reactor model with a novel dual fuel tabulated chemistry model. To evaluate the characteristics of the autoignition in the end gas, the detonation diagram developed by Bradley and co-workers is applied. The single cylinder experiments with direct water injection outline the decreasing carbon monoxide emissions with increasing water content, while the nitrogen oxide emissions indicate only a minor decrease. The simulation results show that the engine can be operated at λ = 1 at full load using water–fuel ratios of up to 60% or cooled low-pressure exhaust gas recirculation rates of up to 30%. Both technologies enable the reduction of the knock probability and the decrease in the catalyst inlet temperature to protect the aftertreatment system components. The strongest exhaust temperature reduction is found with cooled low-pressure exhaust gas recirculation. With stoichiometric air–fuel ratio and water injection, the indicated efficiency is improved to 40% and the carbon monoxide emissions are reduced. The nitrogen oxide concentrations are increased compared to the fuel-rich base operating conditions and the nitrogen oxide emissions decrease with higher water content. With stoichiometric air–fuel ratio and exhaust gas recirculation, the indicated efficiency is improved to 43% and the carbon monoxide emissions are decreased. Increasing the exhaust gas recirculation rate to 30% drops the nitrogen oxide emissions below the concentrations of the fuel-rich base operating conditions.

3-D Numerical Study of Effect of Flow Parameters upon the Uniformity of NH3 in Urea-SCR

2012 ◽  
Vol 505 ◽  
pp. 175-179 ◽  
Author(s):  
R. Vikas ◽  
J.M. Mallikarjuna ◽  
V. Ganesan
Keyword(s):  
Catalytic Reduction ◽  
Numerical Study ◽  
Water Solution ◽  
Injection Pressure ◽  
Exhaust Gas ◽  
Oxides Of Nitrogen ◽  
Lean Burn ◽  
Flow Parameters ◽  
Ammonia Slip ◽  
Engine Emission

Nowadays, due to the stringent engine emission norms, an efficient technique is required to reduce oxides of nitrogen (NOX) from automobiles especially from the lean burn engines. Although Urea Selective Catalytic Reduction (SCR) is capable of satisfying these norms, the ammonia slip nullifies its advantages. Ammonia slip is mainly due to the lack of uniformity of ammonia at the monolith entrance. The uniformity of ammonia distribution mainly depends upon the flow parameters of exhaust gas and the injection parameters of urea water solution. The current study addresses the effect of flow parameters, temperature and flow rate of exhaust gas on the injection pressure. The results obtained reveals useful guidelines for enhancing the uniformity of ammonia in Urea-SCR.

Ethanol Lean Combustion Characteristics of a GDI Engine

2015 ◽  
Vol 798 ◽  
pp. 219-223
Author(s):  
Roberto B.R. Costa ◽  
Carlos A.J. Gomes ◽  
Fabricio J.P. Pujatti ◽  
Ramon Molina Valle ◽  
José E.M. Barros
Keyword(s):  
Engine Speed ◽  
Injection Pressure ◽  
Combustion Stability ◽  
Lean Burn ◽  
Engine Efficiency ◽  
Lean Combustion ◽  
Excess Air ◽  
Wide Range ◽  
Ethanol Combustion ◽  
Gdi Engine

In the present study, ethanol combustion analysis was carried in a wall guided type GDI engine, to achieve combustion stability under lean burn operation and to expand the flammability limit for increasing engine efficiency. Tests were performed at constant engine speed, load and injection pressure (1000 rpm, NIMEP = 3 bar, 100 bar), for a wide range of injection, ignition and mixture formation parameters. NISFC, combustion stability, PMEP and burn duration were evaluated at each excess air ratio. An improvement on fuel economy and, consequently, increased engine efficiency was achieved for excess air ratios of λ = 1.1 and λ = 1.2.

Direct Water Injection to Improve Diesel Spray Combustion

2003 ◽  
Author(s):  
Koji Takasaki ◽  
Tatsuo Takaishi ◽  
Hiroyuki Ishida ◽  
Keijirou Tayama
Keyword(s):  
Diesel Engines ◽  
High Speed ◽  
Fuel Injection ◽  
Nox Reduction ◽  
Water Injection ◽  
Injection Pressure ◽  
Injection System ◽  
Injection Hole ◽  
Low Speed ◽  
Direct Water Injection

Now, it is essential to apply some measures for NOx reduction to low-speed diesel engines emitting much more NOx than high-speed engines. At the same time PM emission must be reduced especially when bunker fuel or heavy fuel is burned. This paper describes the applications of SFWI (Stratified Fuel Water Injection) system and DWI (Direct Water Injection) system to large sized diesel engines to reduce NOx and PM emission. SFWI system makes it possible to inject water during fuel injection from the same nozzle hole without mixing the liquids. DWI system injects water with high injection pressure from the other injection hole than the fuel injection hole into the combustion chamber directly. For testing both the systems, a 2-stroke-cycle low-speed test engine was used.

scholarly journals Exhaust Gas Characteristics According to the Injection Conditions in Diesel and DME Engines

2019 ◽  
Vol 9 (4) ◽  
pp. 647 ◽  
Author(s):  
Seamoon Yang ◽  
Changhee Lee
Keyword(s):  
High Pressure ◽  
Injection Pressure ◽  
Common Rail ◽  
Nox Emissions ◽  
Exhaust Gas ◽  
Pilot Injection ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Pressure Injection ◽  
High Pressure Injection

In this paper, the effect of high-pressure injection pressure on particulate matter (PM) and nitrogen oxide (NOx) emissions is discussed. Many studies have been conducted by active researchers on high-pressure engines; however, the problem of reducing PM and NOx emissions is still not solved. Therefore, in the existing diesel (compression ignition) engines, the common rail high-pressure injection system has limitations in reducing PM and NOx emissions. Accordingly, to solve the exhaust gas emission problem of a compression ignition engine, a compression ignition engine using an alternative fuel is discussed. This study was conducted to optimize the dimethyl ether (DME) engine system, which can satisfy the emission gas exhaust requirements that cannot be satisfied by the current common rail diesel compression ignition engine in terms of efficiency and exhaust gas using DME common rail compression ignition engine. Based on the results of this study on diesel and DME engines under common rail conditions, the changes in engine performance and emission characteristics of exhaust gases with respect to the injection pressure and injection rate were examined. The emission characteristics of NOx, hydrocarbons, and carbon monoxide (CO) emissions were affected by the injection pressure of pilot injection. Under these conditions, the exhaust gas characteristics were optimized when the pilot injection period and needle lift were varied.

Biodiesel Combustion and Emissions in Engines Using Modern Common-Rail Fuel Injection Systems

2008 ◽  
Author(s):  
Prashanth K. Karra ◽  
Matthias K. Veltman ◽  
Song-Charng Kong
Keyword(s):  
Fuel Injection ◽  
Injection Pressure ◽  
Exhaust Gas Recirculation ◽  
Common Rail ◽  
Injection System ◽  
Injection Timing ◽  
Fuel Injection System ◽  
Nox Emissions ◽  
Exhaust Gas ◽  
Gas Recirculation

This study performed experimental testing of a multi-cylinder diesel engine using different blends of biodiesel and diesel fuel. The engine used an electronically-controlled common-rail fuel injection system to achieve a high injection pressure. The operating parameters that were investigated included the injection pressure, injection timing, and exhaust gas recirculation rate. Results showed that biodiesel generally reduced soot emissions and increased NOx emissions. The increase in NOx emissions was not due to the injection timing shift when biodiesel was used because the present fuel injection system was able to give the same fuel injection timing. At high exhaust gas recirculation rates, emissions using regular diesel and 20% biodiesel blends are very similar while 100% biodiesel produces relatively different emission levels. Therefore, the increase in NOx emissions may not be a concern when 20% biodiesel blends are used with high exhaust gas recirculation rates in order to achieve low temperature combustion conditions.

scholarly journals Exhaust gas heat recovery through secondary expansion cylinder and water injection in an internal combustion engine

2017 ◽  
Vol 21 (1 Part B) ◽  
pp. 729-743
Author(s):  
Toosi Nassiri ◽  
Amir Kakaee ◽  
Hazhir Ebne-Abbasi
Keyword(s):  
Internal Combustion Engine ◽  
Thermal Efficiency ◽  
Combustion Engine ◽  
Water Injection ◽  
Internal Combustion ◽  
Exhaust Gas ◽  
Exhaust Gases ◽  
Injection Process ◽  
Direct Water Injection ◽  
Novel Concept

To enhance thermal efficiency and increase performance of an internal combustion engine, a novel concept of coupling a conventional engine with a secondary 4-stroke cylinder and direct water injection process is proposed. The burned gases after working in a traditional 4-stroke combustion cylinder are transferred to a secondary cylinder and expanded even more. After re-compression of the exhaust gases, pre-heated water is injected at top dead center. The evaporation of injected water not only recovers heat from exhaust gases, but also increases the mass of working gas inside the cylinder, therefore improves the overall thermal efficiency. A 0-D/1-D model is used to numerically simulate the idea. The simulations outputs showed that the bottoming cycle will be more efficient at higher engines speeds, specifically in a supercharged/turbocharged engine, which have higher exhaust gas pressure that can reproduce more positive work. In the modeled supercharged engine, results showed that brake thermal efficiency can be improved by about 17%, and brake power by about 17.4%.

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