Emissions Of Internal Combustion Engines Research Articles

AI-driven optimization of ethanol-powered internal combustion engines in alignment with multiple SDGs: A sustainable energy transition

With the escalating requirement for global sustainable energy solutions and the complexities linked with the complete transition to new technologies, internal combustion engines (ICEs) powered with biofuels like ethanol are gaining significance over time. However, problems linked to the performance and emissions of such ICEs necessitate accurate prediction and optimization. The study employed the integration of artificial neural networks (ANN) and multi-level historical design of response surface methodology (RSM) to address these challenges in alignment with the Sustainable Development Goals (SDGs). A single-cylinder spark ignition (SI) engine powered with ethanol-gasoline blends at different loads and speeds was used to gather data. Among six initially trained ANN models, the most efficient model with a regression coefficient (R2) of 0.9952 (training), 0.98579 (validation), 0.98847 (testing), and 0.99307 (overall) was employed to predict outputs such as brake power, brake specific fuel consumption (BSFC), brake thermal energy (BTE), concentration of carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen NOx. Predicted outputs were optimized by incorporating RSM. On implementing optimized conditions, it was observed that BP and BTE increased by 19.9%, and 29.8%, respectively. Additionally, CO, and HC emissions experienced substantial reductions of 28.1%, and 40.6%, respectively. This research can help engine producers and researchers make refined decisions and achieve improved performance and emissions. The study directly supports SDG 7, SDG 9, SDG 12, SDG 13, and SGD 17, which call for achieving affordable, clean energy, sustainable industrialization, responsible consumption, and production, taking action on climate change, and partnership to advance the SDGs as a whole respectively.

Comparative study of NH3 and H2 impacts on combustion and emission characteristics of n-Hexadecane under different flame conditions

The addition of renewable fuel to hydrocarbon fuel mitigated the carbon monoxide, carbon dioxide and soot particle emissions of internal combustion engines. A comparative study of the ammonia and hydrogen effect on combustion and emission characteristics of n-hexadecane flames was executed at various flame conditions. The results showed that alternative fuels had a stronger impact on peak temperature at diffusion flame conditions rather than at premixed flame conditions. The premixed flame released carbon monoxide emission lower than the diffusion flames with/without additional fuels. The carbon monoxide emissions decreased highly with ammonia enrichment instead of hydrogen. At premixed and coflow diffusion flame conditions, the ammonia highly reduced carbon dioxide emission compared to hydrogen. Hydrogen addition reduced the nitrogen oxide emission, whereas it was increased by ammonia. The soot particle number density was reduced highly by hydrogen addition instead of ammonia at the premixed flow flame and diffusion coflow flame conditions. The impact of hydrogen on the reduction of soot mass concentration emissions was greater than that of ammonia at all combustion conditions. It is suggested that H2 ≥ 70% should be mixed in n-hexadecane fuel because a higher burning velocity can be achieved with a higher emission reduction. A reduction in the emission of carbon-related species can be realized with a small reduction in burning velocity at NH3 < 70%.

Turpentine as an Additive for Diesel Engines: Experimental Study on Pollutant Emissions and Engine Performance

The need for reducing fossil fuel consumption and greenhouse gas (GHG) emissions in internal combustion engines has raised the opportunity for the use of renewable energy sources. For the progressive replacement of fossil fuels like diesel, those derived from the sustainable management of forest resources may be a good option. In Portugal, pine trees (pinus pinaster) are among the most widely cultivated tree species. Turpentine can be extracted from their sap without harming the tree. Turpentine is known to be a good fuel with a lower viscosity than regular diesel but with a comparable caloric value, boiling point and ignition characteristics, although it is not widely used as a compression ignition fuel. Moreover, recent research has highlighted the possibility of substantially increasing the turpentine yield through biotechnology, bringing it closer to economic viability. The present study investigates the performance, pollutant emissions and fuel consumption of a 1.6 L four-cylinder direct-injection diesel engine operating with several blends of commercial diesel fuel and turpentine obtained from pine trees. The aim of this study was to assess whether it would be possible to maintain or even improve the performance, fuel consumption and GHG and pollutant emissions (HC, NOx, CO and PM) of the engine with the partial incorporation of this biofuel. Turpentine blends of up to 30% in substitution of regular diesel fuel were tested. The main novelties of the present work are related to (i) the careful testing of a still-insufficiently studied fuel that could gain economical attractiveness with the recent developments in yield improvement through biotechnology and (ii) the tests conducted under fixed engine load positions typical of road and highway conditions. The addition of this biofuel only slightly impacted the engine performance parameters. However, a slightly positive effect was observed in terms of torque, with an increase of up to 7.9% at low load for the 15T85D mixture and 6.8% at high load being observed. Power registered an increase of 9% for the 15T85D mixture at low speed and an increase of 5% for the 30T70D mixture at high speed when compared to the reference fuel (commercial diesel fuel). While the efficiency and fossil GHG emissions were improved with the incorporation of turpentine, it had a mixed effect on polluting emissions such as unburned hydrocarbons (HC) and smoke (PM) and a negative effect on nitrogen oxides (NOx). NOx emissions increased by 30% for high loads and 20% for low loads, mainly as an indirect effect of the improvement in the engine performance and not so much as a consequence of the marginally higher oxygen content of turpentine relative to commercial diesel fuel.

Exploring the Potential of Lignocellulosic Biomass-Derived Polyoxymethylene Dimethyl Ether as a Sustainable Fuel for Internal Combustion Engines

The most effective way to reduce internal combustion engine emissions is to use a sustainable alternative fuel that contains oxygen molecules. Alternative fuels may be used to address a future global energy crisis. Different oxygenated alternative fuels have been investigated in internal combustion engines. Polyoxymethylene di-methylene ether (PODE), which contains 3–5 CH2O groups, is currently superior in the field of oxygenated fuels due to its physical and chemical properties. Furthermore, using PODE as a fuel does not necessitate any significant engine modifications. When compared to standard diesel fuel, the use of PODE results in near stoichiometric combustion with less hazardous exhaust gas. It also significantly reduces NOx emissions due to the lack of C-to-C bonds. Several articles in the literature were found on the manufacturing and application processes for the production of PODE. However, the current review focuses primarily on simplifying the various production technologies, the physical and chemical properties of PODEn and its advantages and disadvantages in ICEs, PODEn application in internal combustion engines and its characteristics, PODE spray analysis, and measurements of the fuel’s physical and chemical characteristics. This review emphasizes the fact that PODE can be used as a sole fuel or in conjunction with fossil fuels and advanced combustion technologies. Because C-C bonds and higher oxygen molecules are not available, the trade-off relationship between nitrogen oxides and soot production is avoided when PODEn is used as a fuel, and combustion efficiency is significantly improved.

Hydrogen and ammonia fuelled internal combustion engines, a pathway to carbon-neutral fuels future

Issues such as climate change and ever-increasing global warming have obliged governments and world authorities to comply with stringent regulations on the control of greenhouse gas (GHG) emissions in internal combustion engines (ICEs). Carbon dioxide (CO2), the most produced GHG, has been the major concern of climate change in recent years. To reduce carbon emissions, fuels with lower carbon content, such as alcohol fuels, or fuels with no carbon content, like hydrogen and ammonia, should be taken into consideration to be replaced by fossil fuels in internal combustion engines.

Prediction of the mean turbulence intensity with a thermodynamic model for CNG and gasoline fuels

Combustion is the main parameter that affects efficiency and exhaust gas emissions in internal combustion engines. In this study, the burning speed of gasoline and CNG were investigated quantitatively by calculating the mean value of turbulent consumption speed instead of qualitatively as is usually done. A three-zone quasi-dimensional thermodynamic model based on the measured cylinder pressure was created to calculate the mean value of turbulent consumption speed and turbulence intensity. The mass flow rate of air was kept constant in all experiments as much as possible, and the spark advance was kept constant at each relative air/fuel ratio. Thus, the effect of fuel and combustion chamber design on the consumption speed and turbulence intensity was directly determined. MR shape reached the highest consumption speed and turbulence intensity in all conditions. In the flat geometry, without any bowl, speed continuously decreased differently from the other designs. Natural gas burned clearly faster in the ultra-lean mixture. The increase in turbulence intensity has different effects on CNG and gasoline. The highest value of the mean turbulence intensity was calculated as approximately 3.4 m/s in the MR design. In the ultra-lean mixture, although the mass flow rate of air was constant, the mean value of the turbulence intensity changed in the same combustion chamber. Therefore, it has been determined that the combustion process affects the turbulence intensity. Using the quasi-dimensional thermodynamic model, mean values of the turbulent burning speeds and turbulence intensity might be calculated without having any optical observation and CFD analysis.

Recycling exhaust emissions of internal combustion engines within the gasification systems: Performance and analysis

The current research presents a proposed system for the recycling of the exhaust emissions from internal combustion engines (ICE) inside the air-blown gasification system. A 2D Computational Fluid Dynamics (CFD) model is investigating the novel research idea and further study the combined effects on the gasifier performance. To this end, the numerical model will be validated against wide range of operating conditions. Additionally, the effect of exhaust emissions injection along with air (the gasifying medium) on gasification, carbon conversion, system performance, syngas composition, and yield will be investigated. A new parameter – CB ratio – is defined, which is the exhaust/emissions from ICE gases to the feedstock mass ratio. Optimum values of CB are recommended between (0.05–0.25). The research idea resulted in boosting the yield of H2, and CO by 10.3, and 3.3 mol.% respectively, and correspondingly, higher heating values by 5.8% within the optimum range of CB. For the same range, N2, and CO2 emissions are found to decrease within the gasifier. The exhaust emissions stream with high temperature and rich content of CO2, and H2O resulted in higher turbulence, velocity, and mixing inside the gasifier. Thus, enhanced the gasification reactions i.e., boudouard, and water gas reactions. Moreover, producer gas yield, carbon conversion and gasification efficiencies are found to be 28, 10, and 11% higher than air gasification under the same working conditions respectively. The proposed design (20 kW gasifier) – i.e., small scale industrial gasification unit – is found to consume around 3.5 kg/hr of the ICE emissions. Thus, preserving the environment, reducing CO2 and GHG emissions, and increasing the gasifier performance. The significant outcomes of the study are applicable for different scales of air-blown gasifiers.

Experimental investigation of the effect of hydrogen ratio on engine performance and emissions in a compression ignition single cylinder engine with electronically controlled hydrogen-diesel dual fuel system

In recent years, there has been a rapid transition from internal combustion engines to hybrid and electric vehicles. It is an inevitable fact that the dominance of internal combustion engines in the market will continue for many years due to the charging and battery problems in these vehicles. Therefore, it is an important issue to improve the performance and emissions of internal combustion engines by making them work with alternative energy sources. In this study, hydrogen-diesel dual fuel mode was used in a dual-fuel compression ignition single cylinder engine with common rail fuel injection system and electronically controlled gas fuel system. The study was carried out at constant speed (1850 rpm), different load (3-4.5-6-7.5-9 Nm) and different hydrogen injector opening amounts (1.6-1.8-2.0 ms). The effects of hydrogen energy ratios obtained with different hydrogen injector opening amount on engine performance and emissions were examined. According to the results, it was determined that the in-cylinder pressure values increased at medium and high loads, and the specific energy consumption decreased. When the emission values were examined, it was determined that there was an increase in NO emissions and a significant decrease in other emissions. However, increasing the hydrogen energy ratio above 14% adversely affected engine performance and emissions.

Comprehensive study of diesel engine characteristics of valves coated by titanium nitride (TiN)

Nano-structured coatings have been used to simulate adiabatic engines with the aim of not only reducing heat rejection and thermal fatigue protection of the metallic surfaces but also potentially reducing internal combustion engine emissions. With this research work, the main emphasis is on optimizing the best coating thickness and studying the effects of nano-structured coatings on the engine's fuel consumption and thermal efficiency with the support of varying conditions. Emission measurements of hydrocarbon (HC), nitrogen oxide (NOx), and carbon dioxide (CO2) were also conducted in this study. In this study, the inlet and exhaust valves were coated with titanium nitride (TiN) material, using a magnetron sputtering technique. TiN was deposited at different thicknesses, such as 2, 3, 4, 5, and 6 microns, over the whole surface of the internal and exhaust valves. The results showed that the brake thermal efficiency (BTE) and NOx emissions were increased, and the specific fuel consumption, CO, and HC emissions were decreased for the thermal coated exhaust valve compared to the standard engine. Peak cylinder pressures for 4 µm thick coatings increased by up to 8.30% in the thermal barrier coating (TBC) engine, particularly at high power outputs; however, exhaust gas temperatures were generally lower, indicating noble gas expansion in the power stroke that initiated the peak cylinder pressure rise and impacted BTE, which increased by 1.6%. The result demonstrates that the TiN coating on the valve serves superior performance to the engine up to an optimum coating thickness beyond which the performance drops off. The characteristics are examined by using an experimental setup and measuring experimental values from the setup for different conditions.

Data-Driven Model for Real-Time Estimation of NOx in a Heavy-Duty Diesel Engine

The automotive sector is greatly contributing to pollutant emissions and recent regulations introduced the need for a major control of, and reduction of, internal combustion engine emissions. Artificial intelligence (AI) algorithms have proven to hold the potential to be the thrust in the state-of-the-art for engine-out emission prediction, thus enabling tailored calibration modes and control solutions. More specifically, the scientific literature has recently witnessed strong efforts in AI applications for the development of nitrogen oxides (NOx) virtual sensors. These latter replace physical sensors and exploit AI algorithms to estimate NOx concentrations in real-time. Still, the calibration of the algorithms, together with the appropriate choice of the specific metric, strongly affects the prediction capability. In the present paper, a machine learning-based virtual sensor for NOx monitoring in diesel engines was developed, based on the Extreme Gradient Boosting (XGBoost) machine learning algorithm. The latter is commonly used in the literature to deploy virtual sensors due to its high performance, flexibility and robustness. An experimental campaign was carried out to collect data from the engine test bench, as well as from the engine electronic control unit (ECU), for the development and calibration of the virtual sensor at steady-state conditions. The virtual sensor has, since then, been tested throughout on an on-road driving mission to assess its prediction performance in dynamic conditions. In stationary conditions, its prediction accuracy was around 98%, whereas it was 85% in transient conditions. The present study shows that AI-based virtual sensors have the potential to significantly improve the accuracy and reliability of NOx monitoring in diesel engines, and can, therefore, play a key role in reducing NOx emissions and improving air quality.

Effect of natural and forced charge air humidity on the performance and emissions of a compression-ignition engine operating at high warm altitude

The effect of ambient humidity on the performance and pollutant emissions of internal combustion engines is not considered in the literature despite type-approval criteria are moving closer to real driving conditions. This work analyses experimentally the effects of charge air humidity at high warm altitudes, where the use of exhaust gas recirculation (EGR) is typically lowered and even avoided to recover engine performance at the expense of NOx emissions increase, on the response of a compression-ignition engine under a wide range of steady-state conditions in terms of engine-out emissions and specific fuel consumption. The impact of specific humidity variations within the atmospheric range was analysed by coupling the engine to an altitude simulator with pressure, temperature, and humidity control capabilities. High altitudes and warm & high ambient temperatures were explored (2000 m at 30 °C and 2500 m at 45 °C) to cover ambient specific humidity up to 30 gwater/kgdry_air. In addition, the effects of increasing the specific humidity above the atmospheric levels were considered at 2500 m and 45 °C to emulate forced injection of water in the engine intake line corresponding to 60 gwater/kgdry_air. With this approach, understanding of the role of humidity is provided to highlight its importance as additional ambient property in emission control. In parallel, the assessment of the forced water content increase to control NOx emissions when EGR must be lowered was performed due to the altitude impact on the engine performance and turbocharger limits. The results showed a consistent and significant reduction in engine-out NOx emissions as the ambient humidity increased, reaching up to 300% with respect to the dry case, caused by the decrease in O2 availability due to the water content increase. The benefits of high humidity in NOx emission control at high altitudes when EGR is not feasible were complemented by an improved trade-off with particulate matter emission compared to the standard from EGR use. The results evidenced a reduction in opacity close to 250% for a given engine-out NOx emission when EGR was replaced by water content. By contrast, the slowdown of the combustion process as the fresh air humidity increased deteriorated the specific fuel consumption significantly as the engine load and speed increased. Nevertheless, these penalties ranged from 2 to 2.7% in the worst conditions and showed the same sensitivity for EGR and humidity increases.

On the Use of a Hydrogen-Fueled Engine in a Hybrid Electric Vehicle

Hybrid electric vehicles are currently one of the most effective ways to increase the efficiency and reduce the pollutant emissions of internal combustion engines. Green hydrogen, produced with renewable energies, is an excellent alternative to fossil fuels in order to drastically reduce engine pollutant emissions. In this work, the author proposes the implementation of a hydrogen-fueled engine in a hybrid vehicle; the investigated hybrid powertrain is the power-split type in which the engine, two electric motor/generators and the drive shaft are coupled together by a planetary gear set; this arrangement allows the engine to operate independently from the wheels and, thus, to exploit the best efficiency operating points. A set of numeric simulations were performed in order to compare the gasoline-fueled engine with the hydrogen-fueled one in terms of the thermal efficiency and total energy consumed during a driving cycle. The simulation results show a mean engine efficiency increase of around 17% when fueled with hydrogen with respect to gasoline and an energy consumption reduction of around 15% in a driving cycle.

Towards high efficiency of intelligent charge compression ignition (ICCI) engine by optimizing the high-reactivity fuel injection strategies under medium–high loads

In order to improve the efficiency and inhibit the emissions of internal combustion engines, the intelligent charge compression ignition (ICCI) mode based on in-cylinder dual direct injection has been proposed. The key problem to expand the load range of ICCI is to suppress the rapid heat release caused by the combustion of premixed fuel under medium–high loads. In this paper, the double injection strategies of high-reactivity fuel were applicated to control the heat release progress. The results show that by the application of the double injection strategies of diesel under indicated mean effective pressure (IMEP) of 0.8 and 1.0 MPa, the indicated thermal efficiency (ITE) was improved while in-cylinder maximum pressure and the NOx emissions were reduced. Through a detailed analysis of the double injection strategy under IMEP of 1.2 MPa, the second injection timing and fuel ratio played more important roles in reducing in-cylinder maximum pressure and improving ITE. By optimizing the double strategy of diesel, the ITE under IMEP of 1.2 MPa could reach above 50 %. Meanwhile the in-cylinder maximum pressure maintained around 15.5 MPa, and the maximum of pressure rising rate was lower than 1.2 MPa/oCA.

Model-based optimization of Sliding Rotary Vane Pump for internal combustion engine cooling of heavy-duty vehicles

The reduction of CO2 and pollutant emissions of internal combustion engines (ICEs) keeping their performance close to the expectations is the main driver of the research in the transportation sector. To counteract the global warming issues international governments set strict emission limitations foreseeing severe penalties for exceeding them. The vehicle electrification surely helps to match these stringent requirements, but a net CO2 reduction can be achieved only if the electricity from the grid has low carbon content. This is not the case of most part of the Countries where the fossil fuels are still the main sources of electric energy production. Thus, considering also the still higher cost of the electric vehicles, the technological improvement of ICEs assumes a strategic importance in this transition period. Among the possible interventions ensuring to achieve this aim, the efficiency enhancement of ICE cooling pump is one of the most effective. As matter of fact, it is proven that the replacement of conventional centrifugal pump with Sliding Rotary Vane Pumps (SVRPs) lead to an interesting decrease of fuel consumption and CO2 emissions. Nevertheless, the design of this machines is not straightforward due to the complex thermo-fluid-dynamic phenomena taking place inside their chambers. This aspect is even more critical for wide operating range as in the case of heavy-duty vehicles. Here, high pump revolution speeds could be provided to satisfy the flow rate requirements thus involving efficiency deterioration due to friction losses enhancement. Therefore, to reduce the revolution speed needed by the pump to elaborate the required flow rate, a novel design strategy based on the enhancement of volumetric capability is presented. The pump resulting by this design approach was called Low Speed LS pump which was prototyped and experimentally characterized over a wide set of operating conditions. The indicated cycle was also measured to better assess the fluid-dynamic behaviour of the machine. The experimental results show a maximum efficiency close to 60% in accordance with the best literature results.

Quantitative fluorescence-based imaging of in-cylinder fuel film thickness at kHz frame rates in a production-type direct-injection spark-ignition engine

Incomplete evaporation of liquid fuel films inside the combustion chamber is a major source of soot and particulate emissions in internal combustion engines. In this study, quantitative imaging of liquid fuel films on the cylinder wall is performed by laser-induced fluorescence (LIF) in a single cylinder engine with optical access to the cylinder liner. A four-component surrogate fuel mixed with 0.5% anisole as the fluorescent tracer was directly injected in a single injection into the motored engine. Fuel impinging on the cylinder wall is excited at 266 nm at kHz repetition rates and imaged by a high-speed camera coupled with an image intensifier. Simultaneously, lubricating oil doped with 0.01 mmol/l pyrromethene 567 is excited at 532 nm and imaged with a second camera. The fuel film thickness on the cylinder wall is compared for two different injections timings, 285 and 240°CA before top-dead center. The initial fuel film thickness is similar for both, but evaporation occurs faster for the later injection, such that the film thickness is similar at the time the piston rings reach the fuel films. When the rings scrape the fuel off the wall, it accumulates on top of the first piston ring and is partly transported downwards to the second and third ring. In the simultaneous oil image, washout of lubricating oil is seen.

Nitrated-, oxygenated- and parent polycyclic aromatic hydrocarbons in organic film on ferries in huangpu river (Shanghai) and source indications of ship-stack emission

Contamination information are desired to fill the gap in the understanding of environmental effects by parent-, nitrated- and oxygenated PAHs (p, n, o-PAHs) from ship stacks. In this study, the organic films on ferries along Huangpu River, one of the busiest inland rivers around the world, were measured seasonally and the compartmental concentrations were rebuilt through a fugacity model to this end. Results revealed that considerable levels of p, n, o-PAHs could be detected in the ferry films. Few seasonal or spatial variations were observed, which indicated a dominant emitter existing in the environments along the river. The compositions of p, n, o-PAHs could be associated with internal combustion engine emissions, however, the composition was different to contamination patterns of on-road traffics. Accordingly, the ship-stack exhausts were suggested to be the primary contributor of p, n, o-PAHs in ferry films. The results of PCA and PMF showed that InP and BghiP could represent the ship-stack PAHs along Huangpu River. Our study highlights a dramatic contribution of ship activities to the contaminations along Huangpu River and provides supports for the usage of organic films on ships as a representative ‘sampler’ of ship-stack emissions.

Analysis of the exhaust hydrogen characteristics of high-compression ratio, ultra-lean, hydrogen spark-ignition engine using advanced regression algorithms

• Exhaust H 2 and NO x were investigated using heavy-duty, hydrogen spark-ignition engine. • Lower excess air ratio exhibited lower H 2 emission, but greater heat transfer loss. • The regression model achieved a high accuracy under various operating conditions. • The proposed H 2 emission model is applicable to various HICEs. Hydrogen is a leading alternative fuel for eliminating the carbon emissions of internal combustion engines. Moreover, the use of hydrogen improves the combustion owing to its high flame speed. The hydrogen selective catalytic reduction is a promising solution for the reduction of nitric oxides (NOx), which is the sole regulated gas species in hydrogen-fueled internal combustion engines. In the present study, hydrogen and NOx emissions, the crucial species for the catalyst performance, were investigated using a heavy-duty, hydrogen spark-ignition engine. The ratio of H 2 to NOx was above 100 at the excess air ratio (lambda) of 2.5 or higher. Three-dimensional, numerical simulation showed that the in-cylinder hydrogen distribution was dependent on the engine load and the lambda value. A regression analysis showed that the exhaust hydrogen quantity had a strong correlation with the seven parameters, namely engine speed, the gross indicated effective pressure (IMEPg), lambda, spark timing, total combustion duration, peak in-cylinder temperature, and peak pressure rise rate. Among these parameters, the IMEPg and the lambda value exhibited the highest weights in a neighborhood component analysis. The regression model with the seven features exhibited the highest R 2 value of 0.94 with the squared exponential Gaussian process regression. The proposed prediction model can contribute to not only reducing NOx emission with aftertreatment, but also maximizing the thermal efficiency of hydrogen-fueled internal combustion engines.

Study on homogeneous charge compression ignition combustion in argon circulated closed cycle hydrogen engine

It is important to improve thermal efficiency and to reduce harmful exhaust gas emissions in internal combustion engines. A closed cycle engine system that uses a monatomic molecular gas as the working fluid can be expected to have high thermal efficiency due to the high specific heat ratio of the gas. Several studies have been reported on closed cycle engines with conventional spark ignition or compression ignition. This research newly proposes an argon circulated closed cycle homogeneous charge compression ignition (HCCI) engine system fueled with hydrogen. In this engine system, effects of in-cylinder gas initial temperature and residual water in recirculated gas on combustion characteristics were investigated. The results show that the system with argon circulation has the wider range of operable conditions and the higher thermal efficiency compared to the case with air as the working fluid.

Experimental and kinetic modeling studies on oxidation of n-heptane under oxygen enrichment in a jet-stirred reactor

Oxygen-enriched combustion can improve thermal efficiency and reduce CO, unburned hydrocarbons and soot emissions in internal combustion engines. There are significant differences in the combustion process and pollutant emissions between oxygen-enriched and air condition. In order to develop an improved understanding of the effect of oxygen concentration on n-heptane oxidation, the jet-stirred reactor oxidation characteristics of n-heptane were experimentally tested at temperatures of 450–950 K and pressures of 1.03 atm with the residence time (τ) of 2 s, under the condition of oxygen mole fractions from 0.055 to 0.6. Meantime, the simulations were performed on CHEMKIN. Results show that, firstly, with the increase of oxygen concentration, the NTC (Negative Temperature Coefficient) effect is weakened, mainly due to the strengthening of low-temperature reaction path, which is also the reason for the improvement of ignition stability in cold-start condition of engines. Secondly, the activity of the reaction system improves with the increase of oxygen concentration. Within 500–750 K, it is due to enhancement of the low-temperature reaction path. When the temperature is higher than 750 K, the improvement is due to the enhancement of decomposition of H2O2 and addition reaction of H and O2. Thirdly, with the increase of oxygen concentration, both the generation and consumption of CO are strengthened, which leads to the tip of the diesel spray flame changing from soot area under air condition to the CO chemiluminescence.

Optimal control of real driving emissions

Real driving emissions (RDE) testing is an important legislative tool to reduce the gap between type-approval and real-world emissions of internal combustion engines. Since low fuel consumption and low nitrogen oxides (NOx) emissions are conflicting objectives, the setpoints of a Diesel engine and its exhaust-gas aftertreatment system have to be optimised and controlled accordingly. To this end, several authors have developed a so-called supervisory controller. In order to comply with RDE legislation, most approaches use a conservative tuning and thus sacrifice performance. In this paper, we explicitly include the RDE requirements in the optimal control problem, which we then solve using direct multiple shooting and nonlinear programming. Using the optimal solution as a benchmark and comparing it to a conservative strategy, we find that fuel savings of up to 3% are possible in simulation. Furthermore, as a first step towards an online, RDE compliant, and optimal supervisory controller, we use Pontryagin’s minimum principle to derive the fact that the optimal costate related to the tailpipe NOx emissions is piecewise constant.