Diesel Engine NOx Research Articles

Predicting NOx emissions in diesel engines via sigmoid NARX models using a new experiment design for combustion identification

Diesel engines are still widely used in heavy-duty engine industry because of their high energy conversion efficiency. In recent decades, governmental institutions limit the maximum acceptable hazardous emissions of diesel engines by stringent international regulations, which enforces engine manufacturers to find a solution for reducing the emissions while keeping the power requirements. A reliable model of the diesel engine combustion process can be quite useful to search for the best engine operating conditions. In this study, nonlinear modeling of a heavy-duty diesel engine NOx emission formation is presented. As a new experiment design, air-path and fuel-path input channels were excited by chirp signals where the frequency profile of each channel is different in terms of the number and the direction of the sweeps. This method is proposed as an alternative to the steady-state experiment design based modeling approach to substantially reduce testing time and improve modeling accuracy in transient operating conditions. Sigmoid based nonlinear autoregressive with exogenous input (NARX) model is employed to predict NOx emissions with given input set under both steady-state and transient cycles. Models for different values of parameters are generated to analyze the sensitivity to parameter changes and a parameter selection method using an easy-to-interpret map is proposed to find the best modeling parameters. Experimental results show that the steady-state and the transient validation accuracies for the majority of the obtained models are higher than 80% and 70%, respectively.

NOx-Conversion Comparison of a SCR-Catalyst Using a Novel Biomimetic Effervescent Injector on a Heavy-Duty Engine

<div class="section abstract"><div class="htmlview paragraph">NOx pollution from diesel engines has been stated as causing over 10 000 pre-mature deaths annually and predictions are showing that this level will increase [<span class="xref">1</span>]. In order to decrease this growing global problem, exhaust after-treatment systems for diesel engines have to be improved, this is especially so for vehicles carrying freight as their use of diesel engines is expected to carry on into the future [<span class="xref">2</span>].</div><div class="htmlview paragraph">The most common way to reduce diesel engine NOx out emissions is to use SCR. SCR operates by injecting aqueous Urea solution, 32.5% by volume (AUS-32), that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water.</div><div class="htmlview paragraph">Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths. The mixer plates create extra exhaust back pressure and cool the exhaust gases, which decreases engine and catalyst efficiency, resulting in overall poor NOx conversion (<40%) and higher CO<sub>2</sub> production under real life drive cycle conditions.</div><div class="htmlview paragraph">To achieve future emission legislation targets, SCR efficiency has to be improved, especially under low catalyst temperature conditions. It should also be noted that Ammonia slip has to be avoided as it is now legislated against [<span class="xref">3</span>].</div><div class="htmlview paragraph">In this study a novel biomimetic effervescent aqueous urea injector, its design inspired by the natural spray phenomenon of the Bombardier Beetle, is used to compare against a market-leading aqueous urea doser in comparable exhaust conditions with and without aggressive mixer plates being installed.</div><div class="htmlview paragraph">The novel biomimetic effervescent injector operates by increasing the temperature of the Urea solution inside a constant volume chamber to its saturated vapour pressure. At the required time of injection an electromagnetically controlled outlet valve opens exposing the now superheated fluid to lower pressure conditions, this results in a hot, effervescent spray being ejected which rapidly breaks up into very fine droplets (<20um) projected at high velocity (60m/s) into the exhaust stream targeted at the face of the SCR catalyst.</div><div class="htmlview paragraph">The novel biomimetic effervescent injector shows great potential with a significant higher NOx conversion rate and lower ammonia slip compared to the market-leading doser on a heavy-duty engine.</div></div>

Recent advances in the preparation of zeolites for the selective catalytic reduction of NOx in diesel engines

Metal-exchanged zeolites with small pore sizes have attracted much attention in recent years due to their application in the selective catalytic reduction (SCR) of NOx in diesel engines.

Simultaneous Application of Exhaust Gas Recirculation and Non-Constant Injection Rates to Reduce NOx and Soot Emissions in Diesel Engines

A combination of EGR and variation of injection rate has been used to keep both NOx and soot emissions at an acceptable level. To do so, a two-dimensional multi-zone phenomenological diesel engine combustion model has been developed. The model consists of several sub-models for spray development, fuel atomization, evaporation, combustion, and emission formation. The fuel spray is divided into several small packets called zones, and consequently, the equations for conservation of mass and energy are solved for each individual zone at each time step, from which the cylinder temperature and pressure are calculated. Additionally, the formation of emissions is tracked as soon as the combustion starts. Moreover, parallel processing programming techniques have been utilized, which reduce the computational time of the model considerably, making it a fast and reliable tool for combustion simulation. Using the model, different rates of EGR are applied, which as expected shows a noticeable decrease in NOx emissions. Thanks to the modular design of the model, injection profile can be changed easily. Instead of using a constant rate injection, three different injection patterns are used. First, an upward step profile is used, in which fuel is initially injected with a lower and then with a higher rate. After that, a downward step profile was applied, which injects the fuel first with a lower and then a higher rate. Finally, a combination of the above profiles is used, i.e., the fuel is injected initially at a low rate, and then, the injection rate is increased, and finally decreased again. It is shown that use of EGR with a combined injection pattern at the same time can keep the NOx and soot emissions of the diesel engine at an acceptable level.

Diesel Engine NOx Emission Modeling Using a New Experiment Design and Reduced Set of Regressors

In this paper, NOx emissions from a diesel engine are modeled with nonlinear autoregressive with exogenous input (NARX) model. Airpath and fuelpath channels are excited by chirp signals where the frequency profile of each channel is generated by increasing the number of sweeps. Past values of the output are employed only in linear prediction with all input regressors, and the most significant input regressors are selected for the nonlinear prediction by orthogonal least square (OLS) algorithm and error reduction ratio. Experimental results show that NOx emissions can be modeled with high validation performance and models obtained using a reduced set of regressors perform better in terms of stability and robustness.

Least Square Adaptation of a Fast Diesel Engine NOx Emissions Model

The paper focuses on the development of an adaptive NOx emissions model, whose intended deployment is to provide accurate estimation, throughout engine lifetime, in correspondence of the engine exhaust port of a Diesel propulsion system. Particularly, black-box modelling approach is proposed, which specifically in this paper takes advantage of an intake manifold oxygen estimator previously developed. The resulting multi-linear regression model was preliminary validated in steady-state conditions. Upon successful verification of model accuracy, the above NOx predictor was integrated within a least-square adaptation algorithm, which relies on the experimental NOx measurement performed downstream the selective catalytic reduction catalyst. Therefore, it was possible to perform further validation analyses, both to assess prediction reliability in transient conditions, as well as to verify the adaptation capability of the proposed least-square-based algorithm.

Performance and NOx Investigation on Diesel Engine using Cold EGR Spiral Tube: A Review

The world has the same problem to reduce emissions. Based the problem, many technologies invented to reduce the Emission. One of them is EGR (Exhaust Gas Recirculation). EGR is the most simpleNOx reduction by circulating potion of exhaust gas return into the combustion chamber. EGR system is often known by the name the hot EGR where exhaust gas circulation process without cooling system. This new Hot EGR system is designed by the addition of cooling system with air-cooled type. So that the circulating of exhaust gas to be cooled in advance in such that the mass of air increases.This research aims to study the performance and a reduction in NOX of diesel engine with EGR using addition of air cooling system. The experiments were used on diesel engine Yanmar TF 85-MHDI

Influence of hydrocarbon species on its adsorption on a VSCR catalyst under simulated diesel engine operating conditions

Vanadia-SCR (VSCR) is a proven technology for reducing diesel engine NOx emissions using urea hydrolysis derived NH3 as a reductant. It is also known that VSCR is active for hydrocarbon (HC) oxidation. However, HC species from diesel engine exhaust may be adsorbed onto VSCR at low exhaust temperatures such as under low engine load or idle conditions. The adsorbed HC may be gradually transformed into more stable coke during engine operation. The accumulated HC or coke on VSCR can result in decreased NOx conversion efficiency due to blockage of catalyst pores and active sites. In addition, rapid oxidation of accumulated HC or coke can lead to exotherms which can thermally damage the VSCR and may lead to vanadium and tungsten release. This work investigates the fundamental adsorption characteristics of HC species on a state-of-the-art VSCR catalyst in the low temperature region. Dodecane and toluene are used as model molecules for alkane and aromatic species from unburned diesel fuel, while squalane is used as a model molecule for unburned lube oil.

NOx emission on-line measurement for the diesel engine based on tunable diode laser absorption spectroscopy

An on-line measurement for the diesel engine NOx emission based on tunable diode laser absorption spectroscopy (TDLAS) technique is realized. Two absorption lines 1900.07059cm−1 and 1626.91952cm−1 are chosen for NO and NO2 measurement. Two ICL inter-band cascade (ICL) lasers are used to measure NO and NO2 separated. In this work, we use the TDLAS system to research the NOx emissions on a four-stroke four-cylinder diesel engine. Optical windows are installed on the exhaust pipe of the diesel engine symmetrical to realize the on-line measurement. The direct detection method is adopted in this work, which can avoid the effect from unknown concentration of particulate matter (PM) in the exhaust. The NOx emission characteristic under different load power and different rotating speed is researched. This work can support the research on the combustion process of diesel engines.

Research on Effect of EGR and SCR on NOX Emission from a Heavy Duty Diesel Engine

Experimental study was conducted on NOX emissions law of a heavy diesel engine with EGR and SCR. Opening of EGR valve (OEV) was adjusted by INCA, and ammonia nitrogen ratio (ANR) was changed by controlling urea injection quantity with control unit DCU of SCR. Under low, medium and high speed and 50%, 75% and 100% load conditions, the effect of EGR (exhaust gas recirculation) and SCR (selective catalytic reduction) on diesel engine NOX emission was studied by test. The results show that when a heavy diesel engine use EGR and SCR, the conversion magnitude and conversion ratio of NO increased significantly, NO_X emissions rule is similar to that of NO, and when opening of EGR valve is more than 25%, the effects of OEV increasing on NO and NO_X are smaller than the effect of SCR. Only under the conditions of high emissions concentrations of NO₂, EGR and SCR significantly reduce NO₂ emission concentration.

Control-oriented premixed charge compression ignition CA50 model for a diesel engine utilizing variable valve actuation

Premixed charge compression ignition (PCCI) is a promising combustion strategy for reducing in-cylinder NOx and particulate matter formation in diesel engines without incurring fuel penalty. However, one of the challenges in PCCI implementation is that the process does not allow direct control of the combustion timing. The crank angle of 50% heat release, known as the CA50, is generally a reasonable proxy for the quality of combustion in terms of maximum pressure rise rate, combustion noise, and fuel conversion efficiency. This paper outlines the development, and validation, of a real-time capable estimation strategy for diesel-fueled PCCI CA50 using production-viable measurements that do not include in-cylinder pressure. The CA50 estimation strategy considers both stages of diesel-fueled PCCI combustion—low-temperature heat release and high-temperature heat release, which contributes most to the cumulative heat released during combustion. The strategy is validated using a PCCI CA50 dataset generated with a wide range of positions of a variable geometry turbocharge, exhaust gas recirculation fractions, and intake valve closing timings. The model estimates CA50 within ±2 CAD for 65 out of 80 data points and exhibits an error standard deviation of 2.55 CAD.

Experimental investigation on NOx and green house gas emissions from a marine auxiliary diesel engine using ultralow sulfur light fuel

In recent years, marine auxiliary diesel engine has been widely used to produce electricity in the large ocean-going ship. One of the main technical challenges for ocean-going ship is to reduce pollutant emissions from marine auxiliary diesel engine and to meet the criteria of disposal on ships pollutants of IMO (International Maritime Organization). Different technical changes have been introduced in marine auxiliary diesel engine to apply clean fuels to reduce pollutant emissions. The ultralow sulfur light fuel will be applied in diesel engine for emission reductions in China. This study is aimed to investigate the impact of fuel (ultralow sulfur light fuel) on the combustion characteristic, NOx and green house gas emissions in a marine auxiliary diesel engine, under the 50%–90% engine speeds and the 25%–100% engine torques. The experimental results show that, in the marine auxiliary diesel engine, the cylinder pressure and peak heat release rate increase slightly with the increase of engine torques, while the ignition advances and combustion duration become longer. With the increases of the engine speed and torque, the fuel consumption decreases significantly, while the temperature of the exhaust manifold increases. The NOx emissions increase significantly with the increases of the engine speed and torque. The NO emission increases with the increases of the engine speed and torque, while the NO2 emission decreases. Meanwhile, the ratio of NO2 and NO is about 1:1 when the diesel engine operated in the low speed and load, while the ratio increases significantly with the increases of engine speed and torque, due to the increase of the cylinder temperature in the diffusive combustion mode. Moreover, the CO2 emission increases with the increases of engine speed and torque by the use of ultralow sulfur light fuel.

Investigating the influence of water injection on the emissions of a diesel engine

There are many methods to decrease the nitrogen oxide emissions of a diesel engine. One promising measure is water injection into the engine’sintake manifold. As emission limits become more and more stringent, the diesel engine NOx–particulate trade-off is a challenge for engine developers. To overcome this challenge, a single-point water injection system has been developed to investigate the influence of different amounts of injected water on the behaviour of a 4-cylinder diesel engine. The amount of injected water was varied from 0 to 100% water-to-fuel ratio in part-load operation (BMEP = 2, 3.5 and 5 bar). The influence on the intake air cooling effect, exhaust emissions, combustion and engine parameters was evaluated. The combustion temperature and the NOx emissions decreased drastically (63% NOx decrease for a BMEP of 5 bar and a waterto-fuel ratio of 100%). This benefit had the drawback of an increase of the particle matter emission at high water-to-fuel ratio. The combustion process and performance parameters regarding efficiency, torque and fuel consumption were marginally influenced by the water injection. This work has achieved a major reduction of NOx raw emissions of a diesel engine. Further research lines could include research on water injection at high load operation points in the engine map.

Study And Evaluation of Injection Timing of CIDI Engine Injection Pump Using Alternate Fuel i.e Biodiesel Fuel

In this investigation an experimental study of the effects of FIP injection timing on Specific Fuel Consumption(SFC), Brake Thermal Efficiency(BTE), Engine Exhaust Gas Temperature(EEGT), CO, HC, NOX and Smoke of “Kirloskar- 6R1080TA, 6-CylinderInline, Direct Injection, Turbocharged Intercooled, 191 hp Diesel Engine” has been conducted. Injection Timing retardation method has been utilised to reduce SFC, EEGT, CO, HC, NOX, Smoke and increase BTE of Kirloskar-6R1080TA Diesel Engine. The Kirloskar 6R1080TA engine has been tested for six different injection timings (23°, 21°, 20°, 19°, 18° and 17° CA BTC) at same engine speeds and load conditions. The SFC,EEGT, CO, HC, NOX and Smoke of engine are approximately higher and BTE lower for injection timings at 23°, 21°, 20°, 18° and 17° CA BTC than 19° CA BTC at same speed and load. The results are showing that SFC,EEGT,CO,HC,NOX and Smoke are approximately reduces and BTE increases by reducing injection timing from 23° CA BTC to 19° CA BTC. Optimum FIP injection timing for Kirloskar 6R1080TA engine has been achieved at 19° CA BTC.

Model based burnt gas fraction controller design of diesel engine with VGT/Dual loop EGR system

-Recently, regulation of NOx and PM emission in diesel engines has become stricter and the EGR system has been expanded into a dual loop EGR system to increase EGR rate as well as to utilize exhaust gas strategically. In terms of engine combustion characteristics, burnt gas fraction is becoming an important factor of solving the NOx and PM emission reduction problem more efficiently but conventional controller focused only pressure and air flow rate targets. Unlike the previous studies, this paper describes a model based burnt gas fraction control structure for a diesel engine with a dual loop EGR and a turbocharger. Feedforward control inputs based on burnt gas fraction states aids in the precise control of diesel engines, especially in transient states by considering coupled behavior within the system. For the controller validation, a control oriented reduced order model of a diesel engine air management system is established to simplify the control input computation and its stability is proved by analysing the internal dynamics stability. Then, a sliding mode controller is designed and controller robustness at certain operating points is validated using an HiLS bench.

Clarification of NH3 Formation Mechanism on a Diesel Engine NOx Storage Reduction Catalyst Under Rich Conditions and Evaluation of the SCR Benefit at WLTC

Recent studies have shown that the combination of a NOx storage reduction catalyst (NSR) and a passive selective catalytic reduction catalyst (pSCR) would be a technical solution to meet post EU6 emission legislation for small passenger cars. In this case, NH3 formed during rich NSR regeneration is used to reduce remaining NOx on a SCR catalyst which is located downstream of the NSR. In this study, first, the NH3 formation mechanism of NSR under different emission λs, rich durations, and stored NOx values are clarified using a diesel engine operating under steady-state operation. Finally, NOx conversion and the associated fuel consumption penalty are clarified under the Worldwide harmonized light vehicle test cycle (WLTC). It was identified that NH3 starts to be produced by the NSR after oxygen storage capacity depletion. Next, a NH3 peak occurs as a result of the converted pre-stored and engine out NOx. If the rich operation is long enough, the pre-stored NOx contribution fades and NH3 concentration lowers to an equivalent level as the engine out NOx. From this understanding, several WLTC patterns were measured varying the number of rich operations and their duration in order to identify best regeneration strategy with a minimum fuel consumption penalty. The optimal pSCR benefit, in terms of fuel penalty, is achieved when the rich operation duration is (1) longer than the breakthrough time, (2) includes the initial NH3 peak resulting from the conversion of the pre-stored NOx.

Decreasing NOx of a Low-Speed Two-Stroke Marine Diesel Engine by Using In-Cylinder Emission Control Measures

The authors applied one-dimensional (1-D) simulation and 3-D Computational Fluid Dynamics (CFD) simulation to evaluate the potential of in-cylinder control methods on a low-speed 2-stroke marine engine to reach the International Maritime Organization (IMO) Tier 3 NOx emissions standards. Reducing the combustion temperature is an important in-cylinder measure to decrease NOx emissions of marine diesel engines. Miller-cycle and Exhaust Gas Recirculation (EGR) are effective methods to reduce the maximum combustion temperature and accordingly decrease NOx emissions. The authors’ calculation results indicate that with a combination of 2-stage turbocharging, a mild Miller-cycle and 10% EGR rate, the NOx emissions can be decreased by 48% without the increased Specific Fuel Oil Consumption (SFOC) penalties; with a medium Miller-cycle and 10% EGR, NOx can be decreased by 56% with a slight increase of SFOC; with a medium Miller-cycle and 20% EGR, NOx can be decreased by 77% and meet IMO Tier 3 standards, but with the high price of a considerable increase of SFOC. The first two schemes are promising to meet IMO Tier 3 standards with good fuel economy if other techniques are combined.

Influence of non-thermal plasma after-treatment technology on diesel engine particulate matter composition and NOx concentration

The effect of non-thermal plasma technology for particulate matter removal and nitrogen oxide emission reduction from diesel exhaust has been investigated. A sample of exhaust was cooled to the ambient temperature and passed through a dielectric barrier discharge reactor. This reactor was employed for producing plasma inside the diesel exhaust. A range of discharge powers by varying the applied voltage from 7.5 to 13.5 kV (peak–peak) at a frequency of 50 Hz has been evaluated during the experiments. Regarding the NOx emission concentration, the maximum removal efficiency has been achieved at energy density of 27 J/L. Soot, soluble organic fraction and sulphate components of diesel particulate matter have been analysed separately, and the consequence of plasma exposure on particle size distribution on both the nucleation and accumulation modes has been studied. Plasma was found to be very effective for soot removal, and it could approach complete removal efficiency for accumulation mode particles. However, when applied voltage approached 12 kV, the total number of nucleation mode particles increased by a factor of 50 times higher than the total particle numbers at the reactor inlet. This increase in nucleation mode particles increased even more when applied voltage was set at 13.5 kV.

The effect of cordierite/Pt catalyst on the NOx reduction in a diesel and Jatropha bio-diesel operated single cylinder engine

Bio-diesel is an alternative energy resource, which can be successfully used in diesel engines. One major disadvantage of using bio-diesel is the higher emission of NOx. Hence some after treatment devices have to be adopted to reduce NOx in order to meet the stringent limits on emission standards. In the current research work honeycomb structured circular Cordierite/Pt SCR catalyst is used as an aftertreatment device. Studies revealed that SCR (Selective catalytic reduction) catalyst exhibits better performance at a higher temperature range (>500°C), which can be successfully used in Trucks and Buses. But many catalysts failed to exhibit better performance at a lower temperature range varies from 180 to 400°C, which makes these catalysts unsuitable to use with light and medium duty vehicles. The main objective of this study is to assess the suitability of Cordierite/Pt catalyst for light and medium duty vehicles and study the effect of SCR catalyst on bio-diesel blends in order to reduce NOx in a single cylinder diesel engine. The experimental work has been carried out using diesel and bio-diesel as a fuel and the NOx reduction is tabulated. The results are validated with CFD code AVL FIRE. The ammonia flow rate has been varied from 0.2 to 0.8kg/h. It has been found that among all the blends B15 has shown maximum NOx conversion of 60% and NH3 conversion of 34%.

Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR

The most promising solution for propulsion of marine vessels currently and for the near future is the two-stroke low-speed diesel engines. Despite its advantages, as far as specific fuel oil consumption, power density and reliability is concerned, it suffers from increased NOx emissions mainly because of its low rotational speed. But the upcoming NOx emission legislation (Tier III) in the marine sector requires considerable reduction of NOx emissions towards levels which have not yet been commercially achieved using primary methods. This creates new challenges for the development and application of innovative techniques that could reduce engine’s NOx emissions with the lowest possible fuel penalty. This is important considering current and future fuel prices. The large size of the 2-stroke marine engine makes the use of experimental techniques, to investigate this potential, expensive and time consuming. Modelling can significantly contribute towards this effort and result to reduction of research and development cost. Among the most effective in-cylinder techniques for NOx reduction is EGR, a proven technology for smaller engines used in the transport sector. In the present study, it is investigated via modelling, the potential to reduce NOx emissions of two-stroke marine engines using EGR. Despite the technological difficulties resulting mainly from the use of Heavy Fuel Oil (HFO), which makes the application of conventional EGR techniques difficult, it is worthwhile investigating the NOx reduction potential, since significant progress has been achieved towards the development of new EGR gas cooling techniques and scrubber technologies for removal of sulphur species from the exhaust gas. The present investigation makes use of an existing well validated multi-zone combustion model, initially developed for high-speed DI diesel engines. The model has been successfully applied in the past, to investigate heavy duty diesel engine NOx reduction via EGR, providing favourable results. Currently it is modified and applied on a two-stroke marine diesel engine using EGR. Model evaluation is based on experimental data acquired from the international literature, due to lack of experimental data for 2-stroke engines. The analysis of derived results reveals model’s ability to predict both engine performance and NOx emissions but most important the ability to predict the overall effect of EGR on NOx emissions in a qualitatively correct way. The results also reveal the strong potential of EGR to control NOx emissions of 2-stroke engines with relatively low fuel penalty compared to alternative techniques.