The continuous pursuit of higher combustion efficiencies, as well as the possible usage of synthetic fuels with different properties than fossil-ones, require reliable and low-cost numerical approaches to support and speed-up engines industrial design. In this context, SI engines operated with homogeneous ultra-lean mixtures both characterized by a classical ignition configuration or equipped with an active prechamber represent the most promising solutions. In this work, for the classical ignition arrangement, a 3D-CFD strategy to model the impact of the ignition system type on the CCV is developed using the RANS approach for turbulence modelling. The spark-discharge is modelled through a set of Lagrangian particles, whose velocity is modified with a zero-divergence perturbation at each discharge event, then evolved according to the Simplified Langevin Model (SLM) to simulate stochastic interactions with the surrounding gas flow.
Water injection (WI) could be a viable tool for the reduction of CO2 emissions of spark-ignition engines. At high loads, the performances of this kind of engines are constrained by knock phenomena, thermal limits of engine components and maximum tolerable in-cylinder pressure. Water injection, mainly due its cooling effect, helps mitigating knock and reducing the exhaust gas temperature. Furthermore, it allows to obtain greater spark advances, better combustion phasing and leaner mixtures with a consequent improvement in terms of engine efficiency. In this work, the authors investigated the effects of a particular direct water injection (DWI) strategy on the performance of a turbocharged PFI spark-ignition engine at high load operation. The analysis has been carried out using a validated 1D model that reproduces the entire engine layout. A knock model allows to identify the knock-limited parameters in the various operating points analyzed.
The development of future gasoline engines is dominated by the study of new technologies aimed to reduce the engine negative environmental impact and increase its thermal efficiency. One common trend is to develop smaller engines able to operate in stoichiometric conditions across the whole engine map for better efficiency, lower fuel consumption and optimal conversion rate of the three-way catalyst (TWC). Water injection is one promising technique, as it significantly reduces the engine knock tendency and avoids fuel enrichment for exhaust temperature mitigation at high power operation. With the focus on reducing the carbon footprint of the automotive sector, another vital topic of research is the investigation of new alternative CO2-neutral fuels or so-called eFuels. Several studies have already shown how these new synthetic fuels can be produced by exploiting renewable energy sources and can significantly reduce engine emissions.
In many Asian countries a significant automobile market share is held by two and three wheelers. Generally, cost and simplicity considerations limit the performance and emission levels of small engines. Methanol is an excellent alternative fuel for SI engines due to its highoctane number, high flame speed, presence of oxygen in its molecule and thus can be used to enhance the performance of small engines. However, use of neat methanol in SI engines poses constraints due to low energy density and poor vaporization characteristics. Also, the effectiveness of methanol as a fuel has still to be thoroughly investigated in small-bore SI engines in order to assess its potential. In this work, a small-bore 200cc three-wheeler automotive engine was modified to operate in the port fuel injection mode with neat methanol as the fuel.
Emission legislation for passenger cars is requiring a drastic reduction of exhaust pollutants. In this framework, achieving a quick heating-up of the catalyst system is of paramount importance to cut down the cold start emissions and meet future regulation requirements. This paper describes the development and the basic characteristics of a novel burner for gasoline engines exhaust systems designed for being activated immediately after cold start. The burner is comprised of a fuel injector, an air system, and an ignition device. The design of the combustion chamber is first presented, with a description of the air-fuel interactions and mixture formation processes. Swirl is used along with a flame-holder concept to anchor the flame at the mixer exit. Spray-swirl and spray-walls interaction are also discussed. Computational Fluid Dynamics (CFD) analyses have been used to guide the design process.
Today’s development of spark ignition engines is driven by reduction of CO2 emissions and increase of efficiency. For many efficiency increasing measures, such as higher compression ratio, downsizing and load shifting the main limitation is the occurrence of knock. Therefore, not only an efficient operating strategy but also appropriate engine design is crucial to account for the phenomenon. This is particularly important for the application of synthetic fuels in order to exploit their full potentail. Investigations of local auto-ignitions preceding knock are crucial to gain a better understanding of the phenomenon and to identify critical engine design to further optimize the geometry. 3D CFD simulations provide the possibility to investigate local parameters in the cylinder during the combustion, whereas 0D simulations do not account for local inhomogeneities.
The transition to electric vehicles in the transportation sector still faces multiple technological challenges and large investments as regards both vehicle design and vehicle charging infrastructure. Therefore, internal combustion engines still dominate such a sector, making the engine improvements, in terms of pollutant emissions and efficiency, essential to mitigate the impact of human activities on the environment. One of the possible approaches to improve the efficiency of internal combustion engines is the recovery of the engine exhaust heat, from both the hot exhaust gases and the engine cooling system. So far, several energy recovery approaches have been explored such as Stirling engines, thermoelectric generators, organic Rankine cycles or inverted Bryton cycles, with encouraging results. One energy recovery technique that has been explored in recent years involves the use of direct injection of H2O under supercritical and superheated conditions.
Abstract The supersession of metallic alloys with lightweight, high-strength composites is popular in the aircraft industry. However, aviation electronic enclosures for large format batteries and high power conversion electronics are still primarily made of aluminum alloys. These aluminum enclosures have attractive properties regrading structural integrity for the heavy internal parts, electromagnetic interference (EMI) suppression, electrical bonding for the internal cells, and/or electronics and failure containment. This paper details a lightweight carbon fiber composite chassis developed at Meggitt Sensing Systems (MSS) Securaplane, with a copper metallic mesh co-cured onto the internal surfaces resulting in a 50% reduction in weight when compared to its aluminum counterpart. In addition to significant weight reduction, it provides equal or improved performance with respect to EMI, structural and flammability performance.
This paper presents a real-time, nonlinear, control-oriented model for a two-stroke, spark-ignition aircraft engine. The safety and reliability of unmanned aerial vehicles (UAVs) are vital for their large-scale usage. Therefore, the design of control systems for normal as well as abnormal operation of UAVs is very essential. Timely detection and isolation of faults in an engine can save the aircraft from catastrophic consequences. Modeling is the first stage in the majority of control methods. This model is designed to be able to accurately and in real-time predict the output of an aircraft engine. Using existing modeling knowledge, a mean-value engine model is developed in this paper. The engine model consists of five submodels named the throttle body model, air dynamics model, fuel dynamics model, rotational dynamics model, and atmospheric model.
Today unmanned aerial vehicle applications are powered by Wankel rotary engines due to their high power-to-weight ratio and smooth operation. Most of modern propulsion units for unmanned aerial vehicles are designed to run on high volatile fuels such as aviation gasoline (AvGas). However, the refueling infrastructure in aviation is geared toward the most used aviation fuel, kerosene. This and other reasons, such as significantly lower price and easier fire protection regulations, lead to the desire to be able to operate these propulsion units with kerosene. Opposed to reciprocating engines, the low compression ratio of rotary engines prevents the implementation of compression ignition combustion processes. Therefore, the purpose of this paper is to discuss the operation of a spark-ignited rotary engine on different fuels. In detail, different qualities of kerosene as well as gasoline/kerosene blends are compared together.
Abstract Knock has been studied by internal combustion engine researchers for well over a century. It remains perhaps the main limit on spark-ignition engine efficiency today. In an engine development environment, knock is typically described through quantification of the high-frequency signal content of cylinder pressure measurements. A cylinder pressure transducer gives a point measurement in the combustion chamber volume. In non-knocking combustion cycles, there is little pressure variation across the chamber; hence, this point measurement adequately represents the average gas pressure acting on the piston. This is not the case for knock where autoignition leads to strong pressure gradients and standing wave behavior or even supersonic shock wave propagation. The resulting pressure signal is complex to interpret.
This SAE Standard establishes the procedure for determining the operator duty cycle sound pressure level Lodc to which operators of powered recreational craft up to 24 m in length are exposed during typical operation as determined by marine engine duty cycle studies. This document describes the instrumentation, the required calibration procedures, the test site, the specifications for “standard craft”, the craft operating conditions, microphone positioning, test procedure, engine speeds for each of the Duty Cycle modes and the formula and table for calculating the Duty Cycle operator ear sound pressure level. This document is subject to change to keep pace with technical advances as well as other international standards and practices. Changes in this Revision: The sound pressure level measurements performed while applying this document are based on the Five-Mode Marine Engine Duty Cycle instead of a single engine speed.
Abstract A numerical simulation is a fundamental tool in the design and optimization procedure of an Internal Combustion (IC) engine; since combustion is the process that mostly influences the engine performance, efficiency and emissions, an effective combustion submodel is fundamental. A simple, nonpredictive way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile that is characterized by a sigmoidal trend; the most used for this purpose is the Wiebe function.
Abstract Homogeneous charge with direct injection (HCDI) is a single-fuel low-temperature combustion (LTC) strategy that injects diesel into the intake port and inside the engine cylinder. The present study aims to numerically evaluate various oxides of nitrogen (NOx) mitigation methods such as split injection, exhaust gas recirculation (EGR), and water vapor induction in a single-cylinder diesel engine operated in HCDI mode. Numerical investigations are carried out using a commercial computational fluid dynamics (CFD) code CONVERGE. Experimental data are generated in a light-duty diesel engine operated in HCDI mode at 2.4 bar indicated mean effective pressure (imep) (low load) and 4.6 bar imep (high load) conditions to validate the CONVERGE predictions. The production engine is modified to run in HCDI mode through suitable modifications in the intake system, cylinder head, and fuel injection systems.
The newly proposed Euro 7 emission standards have added regulations limiting ammonia emissions for gasoline vehicles. This paper proposes a new emissions-control strategy to satisfy the regulated ammonia emission levels, using deceleration cylinder cut-off (DCCO) to reduce or eliminate conventional deceleration fuel cutoff (DFCO) and the associated lean-rich excursions in the three-way catalyst during oxygen saturation and desaturation. The improved air-fuel ratio management closer to stoichiometry lowers the ratio of CO to NOx and thus the ammonia (NH3) formation rate inside catalytic converter. Tests show more than 80% reduction of ammonia emission on the WLTC drive cycle without increasing other regulated emissions.