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The increasing use of downsized turbocharged gasoline engines for passengers cars and the new European homologation cycles (WLTC and RDE) both impose an optimization of the whole engine map. More weight is given to mid and high loads, thus enhancing knock and overfueling limitations. At low and moderate engine speeds, knock mitigation is one of the main issues, generally addressed by retarding spark advance thereby penalizing the combustion efficiency. At high engine speeds, knock still occurs but is less problematic. However, in order to comply with thermo-mechanical properties of the turbine, excess fuel is injected to limit the exhaust gas temperature while maximizing engine power, even with cooled exhaust manifolds. This also implies a decrease of the combustion efficiency and an increase in pollutant emissions. Water injection is one way to overcome both limitations.

In order to assist in fast design cycle of Diesel engines selective catalytic reduction (SCR) exhaust systems, significant endeavor is currently being made to improve numerical simulation accuracy of urea thermo-hydrolysis. In this article, the achievements of a recently developed urea semi-detailed decomposition chemical scheme are assessed using three available databases from the literature. First, evaporation and thermo-hydrolysis of urea-water solution (UWS) single-droplets hanged on a thin thermocouple ring (127 μm) as well as on a thick quartz (275 μm), have been simulated at ambient temperature conditions ranging from 473K to 773K. It has been shown that the numerical results, in terms of evaporation rate and urea gasification, as well as droplet temperature history are very close to the experiments if the heat flux coming from the droplet support is properly accounted for.

In this study, the impact of the intake valve timing on knock propensity is investigated on a dual-fuel engine which leverages a low octane fuel and a high octane fuel to adjust the fuel mixture’s research octane rating (RON) based on operating point. Variations in the intake valve timing have a direct impact on residual gas concentrations due to valve overlap, and also affect the compression pressure and temperature by altering the effective compression ratio (eCR). In this study, it is shown that the fuel RON requirement for a non-knocking condition at a fixed operating point can vary significantly solely due to variations of the intake valve timing. At 2000 rpm and 6 bar IMEP, the fuel RON requirement ranges from 80 to 90 as a function of the intake valve timing, and the valve timing can change the RON requirement from 98 to 104 at 2000 rpm and 14 bar IMEP.

Future pollutant emissions legislations are expected to be increasingly stringent. To reduce Nitrogen Oxides (NOx) emissions produced by Diesel engines, advanced combustion technologies - like Low Temperature Combustion (LTC) -, vehicle hybridization and NOx after-treatment systems - such as Selective Catalytic Reduction (SCR) systems - can be considered, leading to a growing demand for NOx models. In this paper, we present a state-of-art of the different existing NOx models, from the black-boxes to the three-dimensional Computational Fluid Dynamics (CFD) codes. A way to classify these models is proposed. The paper also introduces the current applications for each subgroup of models. Then, a black-box and two grey-box NOx models are studied regarding their accuracy and their sensitivity to model inputs. These models are validated for two Diesel engines on steady-state operating points as well as on transient operations. The semi-physical models accurately predict NOx emissions.

This paper presents the evaluation of the impact of Diesel Exhaust Fluid (DEF) quality on the behavior of a controlled SCR system. Proper control of the Selective Catalytic Reduction system is crucial to fulfill NOx emissions standards of modern Diesel engines. Today, the urea concentration of DEF is not considered as a control system input. Moreover, Urea Quality Sensors (UQS) are now available to provide real time information of Diesel Exhaust Fluid quality. The impact of percent urea from 20 to 36% on the NOx emissions of a passenger car 2.2L Diesel engine is calculated using a reference SCR model and a reference SCR control tool in multiple NEDC transient conditions. Several control tunings are tested with different levels of feedback. Ammonia slip levels are also calculated.

Recent work has demonstrated the potential of gasoline-like fuels to reduce NOx and particulate emissions when used in Diesel engines. In this context, straight-run naphtha, a refinery stream directly derived from the atmospheric crude oil distillation process, has been identified as a highly valuable fuel. The current study is one step further toward naphtha-based fuel to power compression ignition engines. The potential of a cetane number 25 fuel (CN25), resulting from a blend of hydro-treated straight-run naphtha CN35 with unleaded non-oxygenated gasoline RON91 was assessed. For this purpose, investigations were conducted on multiple fronts, including experimental activities on an injection test bed, in an optically accessible vessel and in a single cylinder engine. CFD simulations were also developed to provide relevant explanations.

This paper addresses the robustness of an optimal online energy management for diesel hybrid electric vehicle (HEV). Optimal strategy is based on the Equivalent Consumption Minimization Strategy (ECMS). Optimal torque split between engine and electric motor is found by minimizing fuel consumption and Nitrogen Oxides (NOx) emissions. Online adaptation is made in order to ensure battery charge sustainability and good driveability when driving conditions are unknown. The strategy is tested in simulation over one hundred driving cycles representative of real-world conditions. Results obtained with the online strategy are compared with those of an offline optimal strategy (knowing the driving cycle a priori). Even if a slight degradation is noticed in comparison to optimal case, fuel economy and NOx reduction - provided by hybridization - are conserved with the online strategy.

The proposed Euro 7 regulation aims to substantially reduce the NOx emissions to 0.03 g/km, a trend also seen in upcoming China 6b and US EPA regulations. Meeting these stringent requirements necessitates advancements in Urea/Selective Catalytic Reduction (SCR) aftertreatment systems, with the urea deposit formation being a key challenge to its design. It’s proven that Computational Fluid Dynamics (CFD) can be an effective tool to predict Urea deposits. Transient wall temperature prediction is crucial in Urea deposit modeling. Additionally, fully understanding the kinetics of urea decomposition and by-products solidification are also critical in predicting the deposit amount and its location. In this study, we introduce (i) a novel film boiling model (IFPEN-BRT model) and (ii) a new urea by-product solidification model in the CONVERGE CFD commercial solver, and validate the results against the recent experiments.

Thermal management is a key issue to minimize fuel consumption while dealing with pollutant emissions. It paves the way for developing new methods and tools in order to assess the effects of warm up phase with different drivetrains architectures and to define the most suitable solution to manage oil and coolant temperatures. DEVICE (Downsized hybrid Diesel Engine for Very low fuel ConsumptIon and CO2 Emissions) project consists in designing hybrid powertrain to cut off significantly CO2 emissions. It combines a 2-cylinder engine with an electric motor and a 7-gear dual clutch transmission. Hybridization and downsizing offer a great improvement of fuel economy and it is valuable to study their effects on thermal management. Hence, a dedicated AMESim platform is developed to model the fluids temperatures as well as the energy balance changes due to the powertrain architecture.

As congestion increases and commute times lengthen with the growing urbanization, many customers will look for effective mobility solutions. Two-wheeler are one of the solutions to deal with these issues, in particular if equipped with electrified powertrains for minimized local noise and air pollutant emissions. Scooters powertrain technology is predominantly based on Spark Ignition Engine (ICE) associated with a Continuously Variable Transmissions (CVT) and a Centrifugal Clutch. Nevertheless, even though CVT gives satisfaction in simplicity, fun to drive, cost effectiveness and vehicle dynamics, its efficiency is an undeniable drawback. Indeed, a conventional CVT is wasting more than 50% of ICE effective power in customer driving conditions. Consequently, those vehicles have high fuel consumption relative to their size, and are equipped with overpowered and heavy internal combustion engines, allowing a large area for further improvements.

The Diesel engine has now become a vital component of the transport sector, in view of its performance in terms of efficiency and therefore CO2 emissions some 25 % less than a traditional gasoline engine, its main competitor. However, the introduction of more and more stringent regulations on engine emissions (NOx, PM) requires complex after-treatment systems and combustion strategies to decrease pollutant emissions (regeneration strategies, injection strategies, …) with some penalty in fuel consumption. It becomes necessary to find new ways to improve the Diesel efficiency in order to maintain its inherent advantage. In the present work, we are looking for strategies and technologies to reduce Diesel engine fuel consumption. Based on the observation that large Diesel engines have a better efficiency than the smaller ones, a detailed thermodynamic combustion analysis of one Heavy Duty (HD) engine and two Passenger car (PC) engines is performed to understand these differences.

The challenge for decreasing the emissions of compression ignition engines now remains mainly on NOx control. If the Lean NOx Trap (LNT) and Selective Catalytic Reduction by Urea (Urea-SCR) are very efficient, their extra-cost and management are a major issue for the OEMs. In that context, the selective catalytic reduction by hydrocarbons (HC-SCR) appears to be an interesting alternative solution, with a more limited NOx conversion efficiency but an easier packaging (diesel fuel as a reductant) and a limited price (reasonable coating cost / no PGM). In the framework of the RedNOx project, a prototype catalyst made of 2% silver on Alumina coated on cordierite was manufactured and tested on a synthetic gas bench. In parallel, an exhaust implementation study has been led to ensure the most suited conditions for injection. Thanks to SGB and simulation results, adapted engine tests have been designed and performed.

The present paper is concerned with part of the work performed by Renault, IFPEN and Politecnico di Torino within a research project founded by the European Commission. The project has been focused on the development of a dedicated CNG engine featuring a 25% decrease in fuel consumption with respect to an equivalent Diesel engine with the same performance targets. To that end, different technologies were implemented and optimized in the engine, namely, direct injection, variable valve timing, LP EGR with advanced turbocharging, and diluted combustion. With specific reference to diluted combustion, it is rather well established for gasoline engines whereas it still poses several critical issues for CNG ones, mainly due to the lower exhaust temperatures. Moreover, dilution is accompanied by a decrease in the laminar burning speed of the unburned mixture and this generally leads to a detriment in combustion efficiency and stability.

Meeting Euro 6d NOx emission regulations lower than 80 mg/km for light duty diesel (60 mg/km gasoline) vehicles remains a challenge, especially during cold-start tests at which the selective catalyst reduction (SCR) system does not work because of low exhaust gas temperatures (light-off temperature around 200 °C). While several exhaust aftertreatment system (EATS) designs are suggested in literature, solutions with gaseous ammonia injections seem to be an efficient and cost-effective way to enhance the NOx abatement at low temperature. Compared to standard SCR systems using urea water solution (UWS) injection, gaseous NH3 systems allow an earlier injection, prevent deposit formation and increase the NH3 content density. However non-uniform ammonia mixture distribution upstream of the SCR catalyst remains an issue. These exhaust gas/ NH3 inhomogeneities lead to a non-optimal NOx reduction performance, resulting in higher than expected NOx emissions and/or ammonia slip.

The selective catalytic reduction (SCR) based on urea water solution (UWS) is an effective way to reduce nitrogen oxides (NOx) emitted by engines. The high potential offered by this solution makes it a promising way to meet the future stringent exhaust gas standards (Euro6 and Tier2 Bin5). UWS is injected into the exhaust upstream of an SCR catalyst. The catalyst works efficiently and durably if the spray is completely vaporized and thoroughly mixed with the exhaust gases before entering. Ensuring complete vaporization and optimum mixture distribution in the exhaust line is challenging, especially for compact exhaust lines. Numerous parameters affect the degree of mixing: urea injection pressure and spray angle, internal flow field (fluid dynamics), injector location …. In order to quantify the mixture quality (vaporization, homogeneity) upstream of the SCR catalyst, it is proposed to employ non intrusive optical diagnostics techniques such as laser induced fluorescence (LIF).

The design and the supervision of hybrid electric vehicles (HEV) are strongly coupled. The mutual influence between the optimal components sizing and the optimal operating points choice makes the problem complex. This was previously exposed in literature for spark ignition (SI) HEV. In this paper, we address the same issue for diesel HEV. In this case, the energy management strategy must take nitrogen oxides (NOx) emissions into account in addition to fuel consumption. This paper presents an optimal supervision strategy and its impact on the electric components sizing. The energy management strategy is based on the equivalent consumption minimization strategy (ECMS) using Pontryagin's minimum principle. It allows an adjustable trade-off between NOx and fuel consumption to be minimized. It was validated experimentally with a hardware-in-the-loop test bed.

CNG is one of the most promising alternate fuels for passenger car applications. CNG is affordable, is available worldwide and has good intrinsic properties including high knock resistance and low carbon content. Usually, CNG engines are developed by integrating CNG injectors in the intake manifold of a baseline gasoline engine, thereby remaining gasoline compliant. However, this does not lead to a bi-fuel engine but instead to a compromised solution for both Gasoline and CNG operation. The aim of the study was to evaluate the potential of a direct injection spark ignition engine derived from a diesel engine core and dedicated to CNG combustion. The main modification was the new design of the cylinder head and the piston crown to optimize the combustion velocity thanks to a high tumble level and good mixing. This work was done through computations. First, a 3D model was developed for the CFD simulation of CNG direct injection.

Fuels from crude oil are the main energy vector used in the worldwide transport sector. But conventional fuel and engine technologies are often criticized, especially Diesel engines with the recent “Diesel gate”. Engine and fuel co-research is one of the main leverage to reduce both CO2 footprint and criteria pollutants in the transport sector. Compression ignition engines with gasoline-like fuels are a promising way for both NOx and particulate emissions abatement while keeping lower tailpipe CO2 emissions from both combustion process, physical and chemical properties of the low RON gasoline. To introduce a new fuel/engine technology, investigation of pollutants and After-Treatment Systems (ATS) is mandatory. Previous work [1] already studied soot behavior to define the rules for the design of the Diesel Particulate Filter (DPF) when used with a low RON gasoline in a compression ignition engine.

Recent work has demonstrated the potential of gasoline-like fuels to reduce NOx and particulate emissions when used in compression ignition engines. In this context, low research octane number (RON) gasoline, a refinery stream derived from the atmospheric crude oil distillation process, has been identified as a highly valuable fuel. In addition, thanks to its higher H/C ratio and energy content compared to diesel, CO2 benefits are also expected when used in such engines. In previous studies, different cetane number (CN) fuels have been evaluated and a CN 35 fuel has been selected. The assessment and the choice of the required engine hardware adapted to this fuel, such as the compression ratio, bowl pattern and nozzle design have been performed on a single cylinder compression-ignition engine.

The hydrogen internal combustion engine is a promising alternative to fossil fuel-based engines, which, in a short time, can reduce the carbon footprint of the ground transport sector. However, the high heat release rates associated with hydrogen combustion results in higher NOx emissions. The NOx production can be mitigated by diluting the in-cylinder mixture with air, Exhaust Gas Recirculation (EGR) or water injected in the intake manifold. This study aims at assessing these dilution options on the emissions, efficiency, combustion performance and boosting effort. These dilution modes are, at first, compared on a single cylinder engine (SCE) with direct injection of hydrogen in steady state conditions. Air and EGR dilutions are then evaluated on a corresponding 4-cylinder engine by 0D simulation on a complete map under NOx emission constraint.