In this paper, an experimental evaluation was conducted to determine the effect of engine load, intake pressure, and the O2-to-fuel ratio (λ) on a Semi-Closed Cycle Oxy-Fuel Combustion (SCC-OFC) reciprocating internal combustion engine (RICE). To this end, tests were carried out at low and mid-high loads in a commercial compression ignition (CI) RICE retrofitted to OFC, sweeping intake pressure and λ at a constant temperature while employing water injection for evaporative cooling. On the one hand, it has been demonstrated that the CI engine can operate across a very wide range of EGR rates—up to 95% at low loads—although with excessive O2 dilution, as inherently high cycle pressure means high EGR and high trapped mass. On the other hand, at mid-high loads, suitable O2 concentrations are achieved even at high cycle pressures, thereby enabling efficient combustion. The cycle operating intake pressure is identified as a key variable in the optimization and control of closed-cycle RICEs. Furthermore, it was shown that the exhaust dry CO2 concentration can be isolated from variations in load, water injection, or EGR, maintaining a constant level through the control of λinj. A critical correlation was observed between the quantity of liquid water ingested by the engine and the deterioration of combustion efficiency (an increase in CO and uHC emissions), presenting a fundamental challenge for closed cycles operating with high wet EGR rates. The extended ignition delay caused by OFC CI - RICE offers a promising avenue for the adoption of highly reactive fuels, such as high-cetane biodiesel, paving the way for the integration of biofuels with source CO2 capture directly from the highly concentrated flue gas of SCC-OFC RICEs.

This work examines the behaviour of a spark-ignition engine using oxy-fuel combustion, coupled with an oxygen production cycle based on a mixed ionic-electronic ceramic membrane. Through 1D-0D simulations, two compression ratios are studied: the original ratio of 9.6 and the optimised CR of 20, under various load levels and altitude conditions. The results show that operational limits exist at part-load conditions, where reducing the load without implementing additional control strategies may compromise system performance. It is observed that at low loads, the intake pressure can fall below atmospheric pressure, encouraging the presence of N2 in the combustion process. Additionally, the engine can operate efficiently up to an altitude of 4000 m, although increasing boosting is required to maintain proper membrane conditions. These findings emphasise the importance of load control and the potential need for energy assistance under certain circumstances.

Ammonia, being 17.6% hydrogen by mass, is regarded as a hydrogen carrier and carbon-free fuel as long as its production methods rely on renewable energy sources. The production and combustion of green ammonia do not generate carbon dioxide, offering a promising avenue for substantial reductions in greenhouse gas (GHG) emissions from a well-to-wake perspective. This paper presents a comprehensive methodology for the development and validation of a thermodynamic model for a two-stroke low-speed marine engine incorporating a hybrid ammonia-diesel diffusion combustion system. The simulation tools are rigorously validated using experimental data obtained during diesel operation. Subsequently, the study explores various aspects of the novel ammonia-diesel combustion system, addressing combustion and emissions characteristics. The investigation incorporates diverse simulation scenarios involving direct fuel injection through dedicated valves into the cylinder head of a six-cylinder, turbocharged compression-ignition engine. The engine features two diesel injection valves, employed to initiate the combustion process, and two ammonia injection valves. Simulation scenarios include variations in the injection timing of the pilot diesel injector and the relative orientation of diesel and ammonia sprays. Case C emerges as the preferred configuration, demonstrating superior metrics in terms of combustion stability, air-fuel mixing, and emissions profile compared to other cases. The results indicate a reduction of CO2 emissions of approximately 95% in mass compared to the baseline diesel operation. Furthermore, notable reductions in NOx emissions are observed, preliminarily attributed to the lower flame temperature of ammonia. Despite the appearance of N2O emissions as a result of ammonia oxidation, the overall potential reduction in GHG emissions, in CO2-equivalent terms, exceeds 85% at selected operating points. This work contributes valuable insights into the optimization of cleaner propulsion systems for maritime applications, facilitating the industry’s transition toward more sustainable and environmentally friendly practices.

This study investigates oxy-fuel combustion (OFC) applied to reciprocating internal combustion engines for a flexible Combined Heat and Power (CHP) plant with carbon capture. Utilizing one-dimensional (1-D) modelling software, the engine and associated components are modelled to generate operating maps based on control strategies. Three control loops are employed: a lambda regulator maintaining a constant O-2/fuel ratio, variable Inlet Valve Closing (IVC) adjusting exhaust temperature by varying trapped mass, and a valve regulating intake pressure through exhaust back-pressure, pressurizing the Exhaust Gas Recirculation (EGR) line to control EGR flow. Analysis reveals a correlation between brake efficiency, mechanical power, and Start of Combustion (SoC), while heat production associates more closely with fuel injection. OFC consistently exhibits lower brake efficiency than conventional configurations but yields increased heat at the exhaust.

An oxycombustion spark-ignition engine coupled to an O2 production cycle based on a mixed electronic-ionic ceramic-type membrane is studied in this paper. The exhaust gases drive oxygen production through a heat exchanger network and a set of turbochargers. Initially, a study at medium speed is carried out to determine the influence of the oxygen concentration and the engine compression ratio on the system performance. A 16.3% of fuel consumption reduction is reached when 30% of O2 mass fraction and an engine compression ratio of 20 are implemented when compared with conventional engine operation. Then, a full load study in a wide range of engine speeds is performed, where a maximum fuel consumption reduction of 21% is obtained at high speed (5000rpm) comparing with conventional engine operation. The study shows the whole cycle has demonstrated promising performance parameters at different working conditions (O2 mass fraction, compression ratio, engine load and speed).

Literature suggests that driving style and conditions play a major role in vehicle energy consumption. In this sense, this work focuses on vehicle speed planning using information from the environment, through vehicle-to-infrastructure (V2I), and from nearby vehicles, with vehicle-to-vehicle (V2V) information to reduce fuel consumption over a signalized route. By knowing the traffic lights scenario of the route in advance and the current position and speed of the preceding vehicle, the proposed algorithm decides the ego-vehicle speed profile during a given horizon to minimize fuel consumption. The proposed strategy solves the optimal control problem (OCP) in each prediction horizon through dynamic programming (DP) with a simplified model. The scenario and the optimal solution are updated periodically to make up for scenario prediction and modeling uncertainties. Experimental tests were conducted on a test bench to evaluate the fuel consumption of the simulated speed profile when compared to the preceding vehicle. Results show that a reduction of almost 20% in fuel consumption is possible without penalizing travel time while keeping it real-time (RT) feasible.

Considering the concerns for emissions reduction in the maritime sector, the present paper evaluates, through modeling and simulation, oxy-fuel combustion in a two-stroke ship engine (2SE) and the best production system configuration to obtain the required oxygen (O2). An initial model of a ship engine is calibrated with the engine manufacturer’s data and then adapted to work with O2 as the oxidant to eliminate nitrogen oxide (NOx) emissions and with exhaust gas recirculation (EGR) to control the in-cylinder combustion temperature. Mixed Ionic–Electronic Conducting (MIEC) membranes produce the necessary O2 from the ambient air, which is heated up and pressurized by a heat exchanger and turbocharging coupled system to provide the air conditions required for the proper operation of the MIEC. Several layouts of this system are evaluated for the full load engine operating point to find the optimum O2 production system configuration. Results reveal that the engine operating under oxy-fuel combustion conditions avoids NOx emissions at the expense of higher brake-specific fuel consumption (BSFC) to obtain the original brake torque, and also expels a stream composed exclusively of CO2 and H2O, which facilitates the separation of CO2 from exhaust gases.

The oxy-fuel combustion engine concept with onboard oxygen generation and carbon capture (CC) is studied using as a starting point a baseline oxy-fuel combustion layout coupled to a mixed ionic-electronic conducting membranes for producing oxygen (O2) from the air. A CC system is designed accounting for the flash-out temperatures and the operating pressure of the last CO2 purification step. The proposed engine concept is optimized through the product of useful effective efficiency and engine brake power,which is maximized actuating on the start of injection (SOI) for every assessed gas path layouts. The additional cooling power required by the carbon capture system (CC) is also contemplated . Initially, two approaches are compared when the CC is coupled to the O2 generation unit, including or not an intake cooler. The use of intake cooler yields better engine performance than removing it but increases the cooling power requirements significantly. The extreme results from using or not the intake cooler, indicates that a proper solution could combine both cases, approaching for a different cooling concept. A mixer model is developed to recirculate part of the water condensed in the CC towards the cylinder inlet to lower the intake gas temperature and increase the oxidizer heat capacity ratio. From this layout, an optimum setup for SOI and recirculated water mass flow is found considering the trade-off between additional cooling power and engine performance. Indeed, this case reduces the total ICE additional cooling power required by the exclusive use of an intake cooler by about 27% and improves the engine performance by about 20% in comparison to the lack of intake cooling of the charge flow.

The possibility of applying oxy-fuel combustion to a compression ignition engine (CIE) at different operating points regarding engine speed and load is studied in this work. To do so, a strategy is proposed to extend the load operation map range of a 2.2 L turbocharged and direct-injection CIE under oxy-fuel combustion conditions using mixed ionic-electronic conducting membranes (MIEC) to acquire oxygen (O2) from the air. As nitrogen is not present in the intake flow, nitrogen oxide (NOx) emissions are eliminated, and carbon capture is allowed. The strategy consists of modifying exhaust gas temperature and oxygen-fuel ratio , generating temperature-lambda maps to decide the optimal combination in terms of engine performance. Thus, the system behavior is analyzed at three engine speeds (1250 rpm, 2500 rpm and 3500 rpm) with different load levels and compression ratio (CR) of 20. The baseline engine model is calibrated with experimental data within part-load operation ranges, and an apparent combustion time model calibrated with computational fluid dynamics data is applied to simulate the combustion process under oxy-fuel combustion conditions. Finally, specific parameters are researched to verify whether the system produces enough energy to heat up the MIEC, generating the necessary oxygen. Indeed, a few of them have been found very useful as design parameters for finding out oxy-fuel engine operation limits and estimating MIEC design features.

Oxy-fuel combustion is considered an attractive alternative to reduce pollutant emissions, which uses high-purity oxygen mixed instead of air for combustion processes. However, purchasing large amounts of high-purity oxygen may be unprofitable for certain industrial sectors, discouraging its implementation. Considering this, the potential of an oxygen production cycle for factories using oxy-fuel combustion is studied by performing a thermo-economic analysis where high-purity oxygen, electricity, and natural gas prices are considered. Oxygen is produced by membrane means, where mixed ionic-electronic conducting membranes are used, which require high temperatures and pressure gradients to work properly. A set of turbochargers is implemented, chosen by scaling an off-the-shelf model, what introduces an innovative way of waste energy recovering for improving the performance of the cycle. The whole cycle is powered by waste heat from high temperature flue gases, and it is sized for a ceramic manufacturing factory. In this work, two cases are analysed, differentiated by considering additional heating and the vacuum generation method in the oxygen line. The first case exhibits smaller production levels, although better profitability (31 (sic)t(-1)), whereas the second case displays higher production levels and production costs (33 (sic)t(-1)). Both cases are competitive concerning the average price of high-purity oxygen, supposing an average of 50 (sic)t(-1) in wholesale markets, proving the potential of the proposed alternative for oxygen production. (C) 2022 The Authors. Published by Elsevier Ltd.

In this work, the Global Energy Balance (GEB) of a 1.6 L compression ignition engine is analyzed during WLTC using a combination of experimental measurements and simulations, by means of a Virtual Engine. The energy split considers all the relevant energy terms at two starting temperatures (20°C and 7°C) and two altitudes (0 and 1000 m). It is shown that reducing ambient temperature from 20°C to −7°C decreases brake efficiency by 1% and increases fuel consumption by 4%, mainly because of the higher friction due to the higher oil viscosity, while the effect of increasing altitude 1000 m decreases brake efficiency by 0.8% and increases fuel consumption by 2.5% in the WLTC mainly due to the change in pumping. In addition, GEB shows that ambient temperature is affecting exhaust enthalpy by 4.5%, heat rejection to coolant by 2%, and heat accumulated in the block by 2.5%, while altitude does not show any remarkable variations other than pumping and break power.

As well as new advances in the after-treatment systems are required to achieve the new pollutant emission requirements, new designs of the exhaust line can be considered in order to increase the engine efficiency and the after-treatment effectiveness. In the present work, a one-dimensional gas dynamic model has been used to carry out a simulation study comparing several exhaust insulation solutions. This solutions include the insulation of the exhaust ports, the exhaust manifold, the internal surface of the turbine volute, the turbine external housing, as well as different combinations of these solutions. A transient analysis has been done in order to evaluate the increment in the exhaust gases temperature, fuel economy and pollutant emission levels over the WLTC (Worldwide harmonized Light vehicles Test Cycle) at three different temperature conditions. As a conclusion, a 12% increment in the turbine outlet gas enthalpy can be achieved by insulating both the exhausts ports and the exhaust manifold. Moreover, more than 30% less pollutant emissions are released to the environment with this setup.

This article presents the experimental validation of a complete integrated one-dimensional twin-scroll turbine model able to be used in reciprocating internal combustion engine unsteady simulations. A passenger car with a twin-entry-type turbine has been tested under engine-like pulse conditions by means of a specifically built gas stand. To obtain high-resolution quality data, the turbine and turbine line pipes have been instrumented with mean and instantaneous pressure sensors as well as temperature and mass flow sensors, employing a uniquely designed rotating valve for the pulse generation. This experimental configuration enables to obtain the pressure decomposition in both inlets and outlets of the turbine. Using the experimental data obtained, the model is fully validated, with special focus on the reflected and transmitted components for analysing the performance of the model and its non-linear acoustics prediction capabilities. The model presents a very high degree of correlation with the experimental results, providing a range of errors similar to the uncertainty of the measurements, even in the medium- and high-frequency spectra.

Despite the importance of turbocharged engines with dual-volute turbines, their characteristic maps and fully predictive modeling using 1D gas dynamic codes are not well established yet. The complexity of unsteady flow and the unequal admission of these turbines, when operating with pulses of engine exhaust gas, makes them a challenging system. This is mainly due to the unequal flow admission, which generates an additional degree-of-freedom with respect to well-known single entry vanned or vaneless turbines. This paper has as the main novelty a simple procedure for characterizing experimentally and elaborating characteristic maps of these turbines with unequal flow conditions. This method of analysis allows for easy interpolation within the proposed characteristic maps or conceiving simple models for calculating and extrapolating full performance parameters of dual-volute turbines. Two innovative 0D mean-line models are described that require a minimum quantity of experimental data for calibrating both: the mass flow parameter model and the isentropic efficiency model. Both models are predictive either in partial or unequal flow conditions using as inputs: the mass flow ratio and the total temperature ratio between branches; the blade speed ratio and the pressure ratio in each branch. These six inputs are generally instantaneously provided by 1D gas-dynamics codes. Therefore, the novelty of the model is its ability to be used in a quasi-steady way for dual volute turbines performance prediction. This can be done instantaneously when turbines are calculated operating at turbocharged engines under pulsating and unequal flow conditions.

Oxy-fuel combustion concept is studied in a compression ignition engine (CIE) using Mixed Ionic-electronic Conducting Membranes (MIECs) to separate oxygen (O-2) from air in order to achieve a clean combustion eliminating completely nitrogen oxides (NOx) emissions and enabling upcoming carbon dioxide (CO2) capture. Exhaust gas recirculation (EGR), composed mainly by CO2 and water, is used to control the in-cylinder temperature and exhaust gas wasted energy is recovered for producing the O-2 required by the engine by heating up the MIEC. For this purpose, different engine configurations are analyzed in order to find out an optimum one in terms of energy efficiency and engine performance. Basically, two different EGR control systems (CS) are studied: one with a variable geometry turbine (VGT) on EGR line and other with a VGT on cylinder exhaust line. A simulation software, so-called Virtual Engine Model (VEMOD), is employed in this study to build and analyze the proposed oxy-fuel engine model which is calibrated with experimental data. The engine and its auxiliary components (turbochargers and heat exchangers) are assessed under oxy-fuel combustion conditions for the engine full load operation points from 1250 rpm to 3500 rpm. If compared to a conventional CIE, at high engine speeds the proposed oxy-fuel combustion engine provides similar brake power and indicated efficiency, whereas at low engine speeds, despite of it yields higher brake-specific fuel consumption (BSFC on average, more than 10%), a brake power enhancement (on average, more than 30%) is observed. In any way the breakthrough result is the feasible end of correlation between BSFC and CO2 emissions due to CO2 capture.

In transport applications, reciprocating internal combustion engines still have important advantages in terms of endurance and refueling time and available infrastructure when compared against fuel cell or battery-based powertrains. Although conventional internal combustion engine configurations produce important amounts of greenhouse gases and pollutant emissions, oxyfuel combustion can be used to mitigate to a great extent such emissions, mainly producing NOx-free, CO2 and H2O exhaust gases. However, the oxygen needed for the combustion, which is mixed with flue gases before entering the cylinder, has to be stored in an additional tank, which hinders the adoption of this technology. Fortunately, the latest developments in gas separation membranes are starting to produce extremely-high selectivity and high permeability oxygen-separation membranes. Using the waste heat of the exhaust gases to heat up a mixed ionic-electronic conducting membrane, and feeding it with pressurized air, it is possible to produce all the oxygen needed by the combustion process while keeping the whole system compact. This works presents a design of an oxy-fuel combustion engine with in-situ oxygen production. The numerical simulations show also that this concept keeps a competitive brake specific fuel consumption, while the high concentration of CO2 in the exhaust gases facilitates the introduction of carbon sequestration technologies, leading to potentially carbon-neutral internal combustion engines.

Due to the need to achieve a fast warm-up of the after-treatment system in order to fulfill the pollutant emission regulations, a growing interest has arisen to adopt variable valve timing technology for automotive engines. Several variable valve timing strategies can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to carry out a simulation study comparing several exhaust variable valve actuation strategies. A steady-state analysis has been done in order to evaluate the potential of the different strategies at different operating points. Finally, the effect on the after-treatment warm-up, fuel economy and pollutant emission levels was evaluated over the worldwide harmonized light vehicles test cycle. As a conclusion, the combination of an advanced exhaust (early exhaust valve opening and early exhaust valve closing) and a delayed intake (late intake valve opening and late intake valve closing) presented the best trade-off between exhaust temperature increment and fuel consumption, which achieved a mean temperature increment during low-speed phase of the worldwide harmonized light vehicles test cycle of 27 °C with a fuel penalty of 6%. The exhaust valve re-opening technique offers a worse trade-off. However, the exhaust valve re-opening leads to lower nitrogen oxide (29% less) and carbon monoxide (11% less) pollutant emissions.

Turbocharged engines are the standard architecture for designing efficient spark ignition and compression ignition reciprocating internal combustion engines (ICE). Turbochargers characterization and modeling are basic tasks for the analysis and prediction of the whole engine system performance and this information is needed in quite early stages of the engine design. Turbocharger characteristics (efficiency, pressure ratio, mass flow rates...) traditionally rely in maps of pseudo non-dimensional variables called reduced variables. These maps must be used by reciprocating ICE designer and modeler not only for benchmarking of the turbocharger, but for a multiplicity of purposes, i.e: assessing engine back-pressure, boost pressure, load transient response, after-treatment inlet temperature, intercooler inlet temperature, low pressure EGR temperature, ... Maps of reduced variables are measured in gas-stands with steady flow but non-standardized fluids conditioning; neither temperatures nor flows. In concrete: turbine inlet gas temperature; lubrication-oil flow and temperature; water-cooling flow and turbo-machinery external heat transfer are non-standardized variables which have a big impact in assessing said multiplicity of purposes. Moreover, adiabatic efficiency, heat losses and friction losses are important data, hidden in the maps of reduced variables, which depend on the testing conditions as much as on the auxiliary fluids temperature and flow rate. In this work it is proposed a methodology to standardize turbochargers testing based in measuring the maps twice: in close to adiabatic and in diathermal conditions. Along the paper it is discussed with special detail the impact of the procedure followed to achieve said quasi-adiabatic conditions in both the energy balance of the turbocharger and the testing complexity. As a conclusion, the paper proposes a methodology which combines quasi-adiabatic tests (cold and hot gas flow) with diathermal tests (hot gas flow) in order to extract from a turbocharger gas-stand all information needed by engine designers interested in controlling or 1D-modelling the ICE. The methodology is completed with a guide for calibrating said control-oriented turbocharger models in order to separate aerodynamic efficiency (adiabatic) from heat transfer losses and from friction losses in the analysis of the turbocharger performance. The outsourced calibration of the turbocharger model allows avoiding uncertainties in the global ICE model calibration, what is very interesting for turbochargers benchmarking at early ICE-turbo matching stages or for global system analysis at early control design stages.

This article presents the experimental validation of a quasi-two-dimensional radial turbine model able to be used in turbocharged reciprocating internal combustion engine simulations. A passenger car variable-geometry turbine has been tested under steady and pulsating flow conditions, instrumented with multiple pressure probes, temperature sensors and mass flow sensors. Using the data obtained, a pressure decomposition has been performed. The pressure at the turbine inlet and outlet has been split into forward and backward travelling waves, employing the reflected and transmitted waves to verify the goodness of the model. The experimental results have been used to compare the quasi-two-dimensional radial turbine model as well as a classic one-dimensional model. The quasi-two-dimensional code presents a good degree of correlation with the experimental results, providing better results than the one-dimensional approach, especially when studying the high-frequency spectrum.

In recent years, the interests on transient operation and real driving emissions have increased because of the global concern about environmental pollution that has led to new emissions regulation and new standard testing cycles. In this framework, it is mandatory to focus the engines research on the transient operation, where a Virtual Engine has been used to perform the global energy balance of a 1.6-L diesel engine during a World harmonized Light vehicles Test Cycle. Thus, the energy repartition of the chemical energy has been described with warmed engine and cold start conditions, analyzing in detail the mechanisms affecting the engine consumption. The first analysis focuses on the "delay" effect affecting the instantaneous energy balance due to the time lag between the in-cylinder processes and pipes: as a main conclusion, it is obtained that it leads to an apparent unbalance than can reach more than 10% of the cumulated fuel energy at the beginning of the cycle, becoming later negligible. Energy split analysis in cold starting World harmonized Light vehicles Test Cycle shows that in this condition the energy accumulation in the block is a key term at the beginning (about 50%) that diminishes its weight until about 10% at the end of the cycle. In warmed conditions, energy accumulation is negligible, but the heat transfer to coolant and oil are higher than in cold starting conditions (21% vs 28%). The lower values of the mean brake efficiency at the beginning of the World harmonized Light vehicles Test Cycle (only about 20%) is affected, especially in cold starting, by the higher mechanical losses due to the higher oil viscosity and the heat rejection from the gases. The friction plays an important role only during the first half of the cycle, with a percentage of about 65% of the total mechanical losses and 10% of the total fuel energy at the end of the World harmonized Light vehicles Test Cycle. However, at the end of the cycle, it does not affect dramatically the mean brake efficiency which is about 31% both in cold starting and warmed World harmonized Light vehicles Test Cycle.