Exhaust Gas Recirculation System Research Articles

An experimental insight into optimized biodiesel production and external re-breathing of burned gases on biodiesel combustion

The present research work depicts the optimization of biodiesel production from used frying oil by response surface methodology. It was found that the optimal reaction conditions were 0.75% mass/mass catalyst concentration, 9:1 methanol-to-oil molar ratio, 60 min reaction time and 500 rpm stirrer speed. For these optimal conditions, biodiesel yield of 95.05 ± 0.15% was obtained. This work also attempts to study the effects of burned gases on the combustion characteristics of used frying oil biodiesel (B20) blend. The experiments were conducted in a single-cylinder, 4-stroke, water-cooled, direct injection compression ignition engine attached with electronically controlled exhaust gas recirculation system. The combustion studies were conducted with and without recirculation of 10% cooled and hot burned gases. The study showed that the overall effect of cooled burned gases was to reduce the maximum cylinder pressure by 3% and the maximum pressure rise rate by 2%. The re-circulated cooled burned gases also retarded the auto-ignition timing by 0.64°. On the other hand, the overall effect of hot exhaust gases on the combustion process is to increase the maximum pressure rise rate by 5% and advance the auto-ignition timing by 1.06°.

Evaluating dedicated exhaust gas recirculation on a stoichiometric industrial natural gas engine

Due to the market presence that natural gas has and is expected to have in the future energy sector, research and development of novel natural gas combustion strategies to increase power density, lower total emissions, and increase overall efficiency is warranted. Dilution whether by excess air or by exhaust gas recirculation has historically been implemented on diesel, natural gas, and gasoline engines to mitigate various regulated emissions. In the large industrial natural gas engine industry, excess air dilution or ultra-lean-burn operation has afforded lean-burn engines increased power density and reduced NO x emissions. This advance in technology has allowed lean-burn engines to compete in markets such as electrical power generation which previously they had not been able. However, natural gas engines utilizing a non-selective catalytic reduction system or three-way catalyst must operate under stoichiometric conditions and thus are limited in power density by exhaust gas temperatures. In previous gasoline small engine research, a novel exhaust gas recirculation technique called dedicated exhaust gas recirculation was shown to have a positive impact on engine-out emissions of NO x and unburned hydrocarbons while also lowering exhaust component temperatures. This work seeks to understand the consequences of implementing a dedicated exhaust gas recirculation system on a multi-cylinder stoichiometric industrial natural gas engine. The results of this initial evaluation demonstrate reductions in engine-out NO x and CO emissions and improvements in engine-out exhaust gas temperatures with the dedicated exhaust gas recirculation technique. However, in a low-turbulence combustion chamber, dedicated exhaust gas recirculation significantly lowers the overall rate of combustion and results in significant differences in cylinder-to-cylinder combustion.

Reduction of efficiency penalty for a natural gas combined cycle power plant with post-combustion CO2 capture: Integration of liquid natural gas cold energy

The high energy consumption requirements of the post-combustion CO2 capture (PCC) process of a natural gas combined cycle (NGCC) power plant will result in a significant reduction in power generation efficiency, and the energy integration of the system can effectively reduce power plant efficiency penalties. However, the existence of a large amount of low-temperature waste heat in NGCC power plant is difficult to utilize due to its low temperature. In this paper, the integration of LNG cold energy with NGCC power plant with PCC process is proposed. For the 391 MW NGCC plant with MEA-based PCC system, the impact of the exhaust gas recirculation (EGR) process is firstly considered and a basic case of 35% EGR is obtained. Then the internal energy integration of the NGCC + PCC + EGR system (case 1) reveals that there are a large number of different temperature waste heat sources in the system, and then the dual-pressure ORC is integrated into the system for energy integration (case 2). Finally, in order to integrate the low temperature waste heat that has not yet been utilized and recover the cold energy of LNG, the LNG and the two-stage condensation Rankine cycle are integrated with case 2. The results show that the net power output of case 3 is 17.55 MW higher than that of NGCC + PCC + EGR system, the total efficiency is increased by 2.51%, and the efficiency penalty is reduced to 7.9%. It can be seen that the combination of LNG cold energy and NGCC power plant can effectively improve the power generation efficiency and reduce the energy penalty.

Nonlinear observer-based control design and experimental validation for gasoline engines with EGR

This paper presents a nonlinear observer-based control design approach for gasoline engines equipped with exhaust gas recirculation (EGR) system. A mean value engine model is designed for control which includes both the intake manifold and exhaust manifold dynamic focused on gas mass flows. Then, the nonlinear feedback controller based on the developed model is designed for the state tracking control, and the stability of the close loop system is guaranteed by a constructed Lyapunov function. Since the exhaust manifold pressure is usually unmeasurable in the production engines, a nonlinear observer-based feedback controller is proposed by using standard sensors equipped on the engine, and the asymptotic stability of the both observer dynamic system and control dynamic system are guaranteed with Lyapunov design assisted by the detail analysis of the model. The experimental validations show that the observer-based nonlinear feedback controller is able to regulate the intake pressure and exhaust pressure state to the desired values during both the steady-state and transient conditions quickly by only using the standard sensors.

Effects of Hot Exhaust Gas Recirculation (EGR) on the Emission and Performance of a Single-Cylinder Diesel Engine

With the increment in global demand for energy, there is a need to reduce vehicle emission, which is among the major causes of air pollution around the world. In order to reduce the emissions levels, this study focuses on the effects of hot exhaust gas recirculation (EGR) system on the performance and emissions of a direct injection (DI) diesel engine. The performance studied includes engine power, torque, brake mean effective pressure, fuel consumption and the exhaust emission. The engine used in this study was a single-cylinder, four-stroke engine with an air-cooled system at a rated speed of 3600 rpm with displacement of 0.219 litres. The engine was operated at varying speeds of 1600 to 3600 rpm with different percentages of EGR (5%, 7%, 10% and 15%). Based on the results, it was shown that EGR had decreased the engine brake power and torque while increasing fuel consumption at the same time. The engine with EGR has reduced the emission level of NOx from 800 to 240 ppm and CO2, from 9% to 4%, while increasing the CO from 2% to 4% and UHC from 10 to 100 ppm. Hence, it was concluded that low emission level of NOx and CO2 could be obtained using EGR as it can be used to improve the emission level of a homogeneous charge compression ignition (HCCI) even further in the extension of this study.

Roadside assessment of a modern city bus fleet: Gaseous and particle emissions

In many cities worldwide, modern fleets have been introduced to reduce gaseous and particle emissions from city buses. To date, most emission studies are limited to a few vehicles, making a statistically significant assessment of control options difficult, especially under real-world driving conditions. Exhaust emissions of 234 individual city buses were measured under real-world stop-and-go traffic conditions at a bus stop in Gothenburg, Sweden. The buses comprised models fulfilling Euro III-VI and EEV (Enhanced Environmentally Friendly Vehicle) standards with different engine technologies, fuels, and exhaust after-treatment systems, and also included hybrid-electric buses (HEV). Both gaseous (NOx, CO, HC, and SO2) and size-resolved particle number (PN) and mass (PM) emission factors (EF) were calculated for vehicles using compressed natural gas (CNG), diesel (DSL), Rapeseed Methyl Ester (RME) and Hydro-treated Vegetable Oil (HVO) equipped with various after-treatment technologies, e.g., diesel particulate filter (DPF), selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) systems. The highest median EFPN was obtained from Euro VHEV-HVO-SCR buses (MdEFPN = 18×1014 # kg-1) when their combustion engines were used though 53% of their accelerations were below detection limits indicating the use of their electrical engine. The highest MdEFPM was obtained from the Euro V-DSL-SCR buses (MdEFPM = 150 mg kg-1) and the lowest from EEV-CNG buses (below detection threshold) and Euro VIHEV-HVO- SCR+EGR+DPF buses (MdEFPM = 19 mg kg-1). The highest MdEFNOx was obtained from the Euro V-RME-SCR (MdEFNOx = 30 g kg-1) and Euro VHEV-HVO-SCR buses (MdEFNOx = 24 g kg-1), and the lowest from CNG buses (MdEFNOx = 4.8 g kg-1) and Euro VIHEV-HVO-SCR+EGR+DPF buses (MdEFNOx = 7.4 g kg-1). Hybrid buses can give higher PN emissions compared to traditional diesel engines, likely due to downsized combustion engines. Replacing diesel by biodiesel fuel reduced MdEFPM significantly but increased MdEFNOx which may be due to the higher combustion temperature and oxygen contents of the fuel (for RME). Overall, the EEV-CNG buses performed the best regarding both the MdEF and low contribution to the high emitters. It was also found that a small (5%) proportion of the buses contributed significantly (14-30%) to the total emissions. Identification and monitoring the maintenance of the high emitters in the fleets should be considered for the improvement of air quality.

Meeting future emission regulation at sea by combining low-pressure EGR and seawater scrubbing

In the current study, the environmental performance of the first full-scale combined low-pressure exhaust gas recirculation (EGR) and seawater scrubbing system was investigated thoroughly onboard an LPG carrier operated on high-sulfur HFO. Results clearly show that the chosen approach allows around 70% $$\hbox {NO}_x$$ reduction and simultaneous elimination (98% reduction) of $$\hbox {SO}_x$$ emissions. This would allow compliance both with $$\hbox {NO}_x$$ Tier III and future ECA sulfur regulations, although it would result in minor fuel penalty due to slightly deteriorated combustion (effect of EGR) and increased backpressure (effect of scrubber). The performed chemical analysis of the water samples revealed a fairly good performance of the wash water treatment plant with water samples identified as a good-quality water almost against all measured compounds. The values for pH, turbidity and nitrates were also far below the IMO requirements. However, in terms of certain metals (vanadium, nickel and zinc) and PAHs (fluoranthene and pyrene), the quality of discharge water was somewhat poorer. These compounds also appear to be the main drivers of risk of the environmental damage as was determined by the PEC/PNEC analysis. Here, the sufficient dilution with ambient seawater is essential to bring down the corresponding concentrations to the acceptable levels, although the measured excessive pollution of ambient water in terms of arsenic, copper and molybdenum should be kept in mind. Finally, different sampling procedures (IMO MARPOL and US EPA VGP rules) were practically evaluated providing some ideas for their further improvement, as with wrong sampling the obtained results can be very misleading.

Experimental Investigation on SI Engine Emissions via EGR and Catalytic Converter with Air Injection Mechanism

Exhaust emissions emitted from spark ignition engines cause air pollution, human health hazards and ecological imbalance. Hence, effective curtail of these is an essential task. For this, an experimental evaluation was carried out on emissions and performance characteristics of the four-stroke three-cylinder Maruthi engine at varied brake power. Three different techniques, initially the exhaust gas recirculation (EGR) system was coupled to the test engine and varied from 0 to 10% for estimation of optimal value. Secondly, the provision of the catalytic converter with the copper as a catalyst and finally by the air injection mechanism of 60 l/m into the catalytic converter is executed and evaluated for optimum emission reduction. Also, the combined effect of these techniques on the characteristics was analysed. From the results, it was found that up to an EGR rate of 5%, an enhancement of 2% in brake thermal efficiency and a reduction of 9.5% in brake specific fuel consumption, 21% in carbon monoxide (CO), 19% in un-burnt hydrocarbon (UHC) and 29% in NOx emissions and a further increase in the EGR rate causes performance deterioration. The NOx emissions decreased by 44% at 7% of EGR. The catalytic converter setup alone decreased CO and UHC by 40% and by application of air injection it was 60%. The CO& UHC emissions decreased by 54% &52% respectively at 7% EGR rate combined with the catalytic converter and air injection mechanism.

Levelized cost analysis of microturbine with exhaust gas recirculation and CO2 capture system in Mexico

The effect on the Levelized Cost of Electricity (LCOE) by implementing CO2 capture on a 200 kW microturbine installed at the National Institute of Electricity and Clean Energies (Spanish acronym INEEL) was evaluated. Increasing the CO2 concentration in exhaust gas is a potentially effective method to reduce the high electrical efficiency penalty caused by using the capture system with chemical absorption. In this paper the LCOE achieved with and without Exhaust Gas Recirculation (EGR) of CO2 were compared. Data obtained in experimental tests of the microturbine operating with diesel as fuel on-site were used to validate the simulated performance in Thermoflex, since there is currently no existing natural gas infrastructure. It was assumed that the performance would be similar to the manufacturer's data, although for each fuel the combustor was different. Natural Gas was used in the simulation at 100% load. The CO2 capture plant was simulated using Aspen Hysys with MEA as the solvent at 90% capture of CO2 and 90% purity. Simulations helped to size the equipment and calculate the investment cost of the CO2 capture and EGR systems. The LCOE was compared for CO2 capture and an EGR system at different ratios, showing that the use of EGR with a small scale capture system reduces the LCOE, while reduces the heat duty in the reboiler due to the increase of CO2 in exhaust gases.

Development of a Computational Fluid Dynamics Model for Predicting Fouling Process Using Dynamic Mesh Model

This article presents a comprehensive computational model capable of simulating fouling layer thickness evolution using dynamic mesh model. This computational methodology has been developed to reproduce the deposit generation during fouling process with an innovated work method. Dynamic mesh model, from Ansys Fluent software, and external routines have been used to implement this advanced numerical model which allows to move the boundaries of a region relative to other boundaries of the zone. The displacement of the nodes of the mesh is the mechanism that this model uses to adjust the geometry according to the fouling layer evolution. During the simulation process, the geometry under investigation is modified to reproduce the emergence and gradual change of the fouling layer. Different rules of deposition and removal of the fouling process can be implemented in the proposed algorithm. The direct interaction between fouling expressions and governing equations of the main flow is used to predict deposits formation and growth. In this article, numerical simulations of soot fouling layer formation have been presented. Deposit evolution has been calculated inside different heat exchanger technologies used in exhaust gas recirculation systems to analyze fouling process and to verify the advantages of this new computational strategy.

Using the heat of recirculation gases of the ship main engine by an ejector refrigeration machine for intake air cooling

One of the promising ways in environmentalizing marine internal combustion engines is the neutralization of harmful substances in exhaust gases through particular gas recirculation (EGR-technology). However, the use of such techniques conflicts with the engine's energy efficiency. In the work presented, the scheme-design solution of the exhaust gas recirculation system with using the heat of recirculation gases by an ejector refrigeration machine for cooling the air at the intake of ship's main engine is proposed. The effect of using the heat of recirculation gases for cooling the air at the intake of the engine is analyzed taking into account the changing climatic conditions for a particular vessel's route line. It is shown that the use of an ejector refrigeration machine reduces the air temperature at the entrance of the main engine by 5-15 ° С, which reduces the specific fuel consumption by 0.5-1.5 g/(kW∙h). This reduces emissions of harmful substances when the engine is running with recirculation of gases, in particular, NOx by 30-35%; SOx by 10-12%.

Experimental and numerical study on the influence of cooled EGR on knock tendency, performance and emissions of a downsized spark-ignition engine

Cooled exhaust gas recirculation (EGR) is a viable technique to mitigate the knock occurrence, to improve the fuel consumption and to reduce the nitrogen oxides (NOx) emissions of spark-ignition engines.This work aims at investigating the effects of a low-pressure cooled EGR system on the performance and exhaust emissions of a small-size turbocharged SI engine through numerical and experimental analyses.First, the experiments are carried out at a speed of 3000 rpm and different engine loads. The standard engine calibration is applied at the reference test conditions. Then, the EGR system is activated and the load is controlled by adjusting the plenum pressure and the spark timing. The experimental results are used to validate a 1D engine model, developed in GT-Power™ software. The latter is integrated with “user-defined” sub-models for an accurate description of the in-cylinder processes, namely turbulence, combustion and heat transfer. Maximum EGR benefits over fuel consumption are achieved at low load, thanks to the reduction of the pumping losses. At high load, minor fuel consumption improvements are obtained, mainly arising from a slight increased knock resistance. Furthermore, increasing EGR rate results in a sensible NOx reduction at each engine load, with a slight penalty on the unburned hydrocarbon emission.

Experimental investigation on a 3000 bar fuel injection system for a SCR-free non-road diesel engine

The upcoming Stage V emissions regulation for Non-Road Heavy Duty Diesel Engines will force OEMs to adopt Diesel Particulate Filters, adding a further degree of complexity to the aftertreatment system, which in several cases already includes specific devices for NOx reduction. Since complex aftertreatment systems can rise packaging problems as well as reliability issues, the authors evaluated the performance of a Stage V compliant engine layout which can avoid dedicated aftertreatment devices for NOx. This engine features a low pressure exhaust gas recirculation system, a two-stage turbocharger and a 3000 bar injection pressure-capable fuel injection system. This paper focus on the experimental assessment of the performance of the fuel injection system, demonstrating how increasing the rail pressure from 2000 to 3000 bar can dramatically improve the NOx-Soot and NOx-Particulate Number trade-off, together with the engine efficiency, without adversely affecting the emission of nanoparticles. In particular, extremely high injection pressures in conjunction with the use of after injection as a soot reduction technique, was found to be capable of achieving a 50% smoke reduction with a more than acceptable engine efficiency degradation.

Influence of Fuel Injection, Turbocharging and EGR Systems Control on Combustion Parameters in an Automotive Diesel Engine

Indicated pressure diagrams were measured during experimental campaigns on the control of fuel injection, turbocharging and hybrid exhaust gas recirculation systems in an automotive downsized diesel engine. Three-part load operating conditions were selected for four test sets, where strategies aimed at the reduction of NOX emissions and fuel consumption, limiting penalties in soot emissions and combustion noise were applied to the selected systems. Processing of in-cylinder pressure signal, its first derivative and curves of the rate of heat release allowed us to evaluate seven parameters related to the combustion centre and duration, maximum values of pressure, heat release and its first derivative, heat released in the premixed phase and a combustion noise indicator. Relationships between these quantities and engine operating, energy and environmental parameters were then obtained by referring to the four test sets. In the paper, the most significant links are presented and discussed, aiming at a better understanding of the influence of control variables on the combustion process and the effects on engine behaviour. The proposed methodology proved to be a consistent tool for this analysis, useful for supporting the application of alternative fuels or advanced combustion modes.

On-board generation of hydrogen to improve in-cylinder combustion and after-treatment efficiency and emissions performance of a hybrid hydrogen–gasoline engine

Abstract Hydrogen on-board fuel reforming has been identified as a waste energy recovery technology with potential to improve Internal combustion engines (ICE) efficiency. Additionally, can help to reduce CO2, NOx and particulate matter (PM) emissions. As this thermochemical energy is recovered from the hot exhaust stream and used in an efficient way by endothermic catalytic reforming of petrol mixed with a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the petrol fed to the reformer and is recirculated to the intake manifold, which will be called reformed exhaust gas recirculation (rEGR). The rEGR system has been simulated by supplying hydrogen (H2) and carbon monoxide (CO) into a conventional Exhaust Gas Recirculation (EGR) system. The hydrogen and CO concentrations in the rEGR stream were selected to be achievable in practice at typical gasoline exhaust temperatures (temperatures between 300 and 600 °C). A special attention has been paid on comparing rEGR to the baseline ICE, and to conventional EGR. The results demonstrate the potential of rEGR to simultaneously increase thermal efficiency, reduce gaseous emissions and decrease PM formation. Complete fuel reformation can increase the calorific value of the fuel by 28%. This energy can be provided by the waste heat in the exhaust and so it is ideal for combination with a gasoline engine with its high engine-out exhaust temperatures. The aim of this work is to demonstrate that exhaust gas fuel reforming on an engine is possible and is commercially viable. Also, this paper demonstrates how the combustion of reformate in a direct injection gasoline engine via reformed Exhaust Gas Recirculation (rEGR) can be beneficial to engine performance and emissions.

High-pressure versus low-pressure exhaust gas recirculation in a Euro 6 diesel engine with lean-NOx trap: Effectiveness to reduce NOx emissions

Exhaust gas recirculation can be achieved by means of two different routes: the high-pressure route (high-pressure exhaust gas recirculation), where exhaust gas is conducted from upstream of the turbine to downstream of the compressor, and the low-pressure one (low-pressure exhaust gas recirculation), where exhaust gas is recirculated from downstream of the turbine and of the aftertreatment system to upstream of the compressor. In this study, the effectiveness of both exhaust gas recirculation systems on the improvement of the NOx-particulate matter emission trade-off has been compared on a Euro 6 turbocharged diesel engine equipped with a diesel oxidation catalyst, a lean-NOx trap, and a diesel particulate filter. Emissions were measured both upstream and downstream of the aftertreatment system, at different combinations of engine speed and torque (corresponding to different vehicle speeds), at transient and steady conditions, and at different coolant temperatures as switch points to change from high-pressure exhaust gas recirculation to low-pressure exhaust gas recirculation. It was shown that low-pressure exhaust gas recirculation was more efficient than high-pressure exhaust gas recirculation to reduce NOx emissions, mainly due to the higher recirculation potential and the lower temperature of the recirculated gas. However, such a differential benefit decreased as the coolant temperature decreased, which suggests the use of high-pressure exhaust gas recirculation during the engine warm-up. It was also shown that the lean-NOx trap storage efficiency decreased more rapidly at high engine load than at medium load and that such reduction in efficiency was much faster when high-pressure exhaust gas recirculation was used than when low-pressure exhaust gas recirculation was used.

Theoretical assessment of integration of CCS in the Mexican electrical sector

This research evaluates the current most advanced and proven Gas Turbine (GT) technologies in a 1 × 1 scheme (400 MW on average) for their application in CO2 capture schemes. It has been demonstrated that the minimum energy required for the separation of CO2 is higher in a Natural Gas Combined Cycle (NGCC) than in a coal-fired power plant. Therefore, existing schemes were evaluated to assess the increased CO2 content in the Exhaust Gases (EG) for a NGCC in order to help reduce the energy penalty and the investment cost in CO2 capture systems. The schemes analyzed were: Exhaust Gas Recirculation (EGR), Evaporative Gas Turbine (EvGT), Supplementary Firing Combustion (SFC), External Firing combustion (EFC) and alternating systems with Selective Exhaust Gas Recycle (S-EGR) and hybridization. The most common GTs used in Mexico: Mitsubishi (15%), Siemens (41%) and General Electric (GE) (44%) including M − 501 GAC, SGT6-8000H and GE7HA.01 models were evaluated in Thermoflex 26®. For these, Levelized Costs of Electricity (LCOE) of 31.46, 31.18 and 31.05 USD/MWh, respectively, were obtained. GE offers the lowest LCOE and the EGR system presented the lowest energy penalty when the CO2 capture system was modeled in HYSYS V8.6®. Implementation of EGR helped to improve the energy efficiency of the NGCC and increased the content of CO2 from 4.2 to 7.1 mol% at 40%EGR. Similarly, EGR helped to reduce the LCOE in the integrated system with CO2 Capture by 10 USD/MWh.

Validation and sensitivity analysis of an in-flow water condensation model for 3D-CFD simulations of humid air streams mixing

The mixing of gaseous streams at different humidity and temperature conditions may generate bulk condensation, which is a particular thermodynamic process that usually implies a great computational effort. A model that provides in-flow condensation predictions without heavily impacting on the simulation time becomes a potential tool for studying situations where the presence of water droplets is a problem. For instance, in a Long-Route Exhaust Gas Recirculation (LR-EGR) system, intake fresh air is mixed with humid and hot exhaust gases, generating water droplets that may impact on the turbo-compressor impeller and produce harmful erosion. Serrano et al. [1] developed a condensation submodel for such purpose. In this work, the 3D CFD methodology is analyzed by means of sensitivity studies on the numerical setup and intake throttle valve angle. Validation of the model is addressed by means of measurements in a fully instrumented continuous flow turbocharger test bench, obtaining quantitative and qualitative agreement. Particularly, a consistent correlation was found between predicted condensation rate and the impeller damage for seven LR-EGR configurations. Moreover, the T-joint geometry is noticed to have a great impact on condensation generation, thus showing the potential of such a 3D model for improving the LR-EGR design.

ЗМЕНШЕННЯ ВИКИДІВ ОКСИДІВ АЗОТУ З ВІДПРАЦЬОВАНИМИ ГАЗАМИ СУДНОВИХ ДИЗЕЛІВ

Solving the problem of ocean's airspace polluting with harmful emissions of ship-generated diesel engines by exhaust gases is associated with the creation of highly effective technologies for the neutralization of nitrogen oxides NOx from the diesel plant that apply both to vessels in service, designed and built. The air entering the engine is a working fluid that carries out a certain thermodynamic cycle, resulting in a change in its chemical composition, and the exhaust gas mixture contains many components. Emissions of harmful substances during the combustion of marine fuels are limited in accordance with international programs for the protection of the atmosphere and requirements of the International Maritime Organization IMO. Requirements apply all groups of harmful emissions of marine engines. The most stringent of them concern nitrogen oxides NOx and sulfur oxides SOx. To reduce harmful emissions from the exhaust gases into the environment, scientists and world leaders in engine construction, such as MAN Energy Solutions and Wärtsilä, apply and offer a variety of techniques to reduce the number of harmful substances in the exhaust gases. One of the most promising is the exhaust gas recirculation system (EGRS) of the ship diesel engine. Its advantage over other methods is the insignificant impact on the operation of the engine. During the exhaust gas recycling a temperature of the flame in the combustion chamber decreases, which leads to the reduction of NOx number. This is a consequence of the high rates of carbon dioxide and water vapor. Since the combustion rate is reduced, the exhaust temperature and the thermal load on the engine part are increased. The dilution of the inflow air with waste gas reduces the oxygen content in the supercharged air from 21 to 13%. The possibilities of the technology of the system of recirculation of exhaust gases of a marine engine are limited by the value of the ratio of O2/CO2 in the intake air, due to which the amount of combustion products at the inlet is limited to no more than 30%

Evaluation of Heavy- and Medium-Duty On-Road Vehicle Emissions in California's South Coast Air Basin.

Emission measurements were collected from heavy-duty (HDVs) and medium-duty vehicles (MDVs) at the Peralta weigh station long-term measurement site near Anaheim, CA, in 2017. Two Fuel Efficiency Automobile Test units sampled elevated and ground-level exhaust vehicles totaling 2 315 measurements. HDVs (1844 measurements) exhibited historical reductions in fuel specific oxides of nitrogen (NOx) from the 2008 measurements (55%) with increased use of exhaust gas recirculation and selective catalytic reduction systems. However, as these technologies have aged, the in-use benefits have declined. Infrared % opacity measurements of tailpipe soot decreased 14% since 2012 with increased diesel particulate filter (DPF) use, DPF longevity, and fleet turnover. Sixty-three percent of the HDV fleet in 2017 was chassis model year 2011+ compared to only 12% in 2012. The observed MDV fleet (471 measurements) was 1.4 years older than the HDV fleet with average NOx 14% higher. A significant reduction in MDV NOx occurred ∼2 model years prior to similar HDV reductions (2014 versus 2016 chassis model year). MDV chassis model years 2014+ were able to meet their corresponding NOx laboratory certification standards in-use, whereas HDVs remain slightly above this threshold. Similar MDV NOx emission trends were also observed in data previously collected in Chicago, IL.