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Abstract CNG is at present retaining a growing interest as a factual alternative to traditional fuels for SI engines, thanks to its high potentials in reducing the engine-out emissions. Increasing thrust into the exploitation of NG in the transport field is in fact produced by the even more stringent emission regulations that are being introduced into the worldwide scenario. Moreover, the transport sector accounts for the 27% of the overall energy consumptions and up to the 13% in terms of global emissions. The present paper aims at deeply investigating into the potentials of a heavy-duty engine running on CNG and equipped with two different injection systems, an advanced single point (SP) one and a prototype multi-point (MP) one. The considered 7.8-liter engine was designed and produced to implement a SP strategy and hence modified to run with a dedicated MP system.

Abstract Homogeneous lean operation is a well-known strategy for enhancing the thermal efficiency of SI-engines. At higher load points the efficiency is often compromised by the need to suppress knock. Experiments were performed to determine the knock characteristics of SI engines using homogeneous lean operation at λ values of up to 1.8 with various hardware configurations that are commonly used to increase the lean limit. Changing λ altered the eigenfrequencies of the combustion chamber and the highest energy excitation mode. Increasing λ from 1.0 to 1.2 increased the knock tendency and led to an earlier knock onset. However, further increases in λ significantly reduced the knock tendency and retarded the knock onset. The knock signal energy increased for higher λ values and constant knock tendencies. The differences in knock characteristics between the various λ values became more pronounced upon raising the intake temperature from 40 °C to 90 °C.

Abstract The main objective of active downsizing is to increase the power train efficiency. In order to consistently enhance an approach of active downsizing, it is inevitable to disable and additionally to disengage part of the overall engine displacement volume. The disengagement avoids the friction loss of the piston group as well as its crank- and valve-train section. Therefore, this beneficial approach, the Split-Crankshaft Engine (SCE) is currently under development at the Chair of Internal Combustion Engines in cooperation with the Gear Research Centre (FZG), at the Technical University of Munich. The SCE concept consists of two partial internal combustion engines, which are arranged inline. The Primary Engine (PE) is permanently running while the Secondary Engine (SE) can be switched on and off load-dependently during driving operation.

Abstract Turbulent jet ignition (TJI) is a pre-chamber initiated combustion technology that has been demonstrated to provide low temperature, faster burn rate combustion of lean and intake charge diluted air-fuel mixtures. Dual mode turbulent jet ignition (DM-TJI) is a novel concept wherein a separate air supply is provided for the pre-chamber apart from the conventional auxiliary fuel as supplied for TJI systems. The current study aims to extend the lean flammability limit of a gasoline-fueled engine using DM-TJI. Ignition delay time and combustion behavior of ultra-lean iso-octane/air mixture (Lambda ≅ 3.0) was studied using a TJI-based optically accessible rapid compression machine. High-speed fuel spray recordings in the pre-chamber were obtained using borescope imaging setup. Images of the reacting turbulent jet and subsequent combustion in the main chamber were captured using a visible color camera.

Abstract Upcoming engine generations are characterized by both a general trend of increased specific-power and higher efficiency. This leads to increased thermal loads, compromising reliability, and simultaneously to a limited amount of heat under ordinary engine use. Heat is a valuable resource in providing passenger comfort and emission control. For these reasons the subject of engine thermal management is receiving increasing attention. This work presents a comprehensive study of the complete engine thermal behavior at relevant running conditions: rated-power, peak-torque and ordinary use. The work is further extended to the engine warm-up period. The result is a high-resolution complete engine thermal model, capable of simultaneously reporting the local temperature of any engine part, and the global engine heat balance at any engine load.

Abstract The influence of the intake valve lift of two Miller cycles on the in-cylinder flow field inside a DISI engine is studied experimentally since changes of the engine flow field directly affect the turbulent mixing and the combustion process. For the analysis of the impact of the valve timing on the general flow field topology and on the large-scale flow structures, high-speed stereo-scopic particle-image velocimetry measurements are conducted in the tumble plane and the cross-tumble plane. The direct comparison to a standard Otto intake valve lift curve reveals evidently different impacts on the flow field for both Miller cam shafts. A Miller cycle that features late intake valve closing shows a flow field comparable to the standard Otto valve timing and a tumble vortex of strong intensity can be identified.

Abstract The proven impact of combustion chamber deposits, CCD, on advanced compression ignition, ACI, combustion strategies has spurred researchers to develop thermal barrier coatings, TBC, which can mimic CCD benefits on combustion efficiency and operational range expansion. However, application of TBCs within multi-mode engines exposes them to non-negligible soot radiation. In the present paper, the impact of radiation heat transfer on combustion chamber deposits is studied. The morphological construction of the combustion chamber deposit layer is shown to be partially transparent to radiation heat transfer, drawing corollaries with ceramic-based TBCs. Additional experimentation eliminates the optical transparency of CCD to reveal an “effective radiation penetration depth” facilitated by open surface porosity. The effective radiation penetration depth is then utilized to establish the relative communicating porosity of CCD and a magnesium zirconate TBC.

Abstract Knurling joint applied in assembled camshaft has developed rapidly in recent years, which have exhibited great advantages against conventional joint methods in the aspects of automation, joint precision, thermal damage, noise, and near net shape forming. Both quality of assembly process and joint strength are the key requirements for manufacturing a reliable assembled camshaft. In this article, a finite element predictive approach including three subsequent models (knurling, press-fit and torsion strength) has been established. Johnson-Cook material model has been used to simulate the severe plastic deformation of the material. The residual stress field calculated from the knurling process was transferred as initial condition to the press-fit model to predict the press-fit load. The predicted press-fit load, torque strength and displacement of cam profile before failure were calculated.

Abstract Fluid mechanical design of the cylinder charge motion is an important part of an engine development. In the present contribution an intake port geometry is proposed that can be used as a test case for intake port flow simulations. The objective is to fill the gap between generic test cases, such as the backward facing step or the sudden expansion, and simulations of proprietary intake ports, which are barely accessible in the community. For the intake geometry measurement data was generated on a flow-through test bench and a wall-modeled LES-simulation using a hybrid RANS/LES approach for near-wall regions was conducted. The objective is to generate and analyze a reference flow case. Since mesh convergence studies are too costly for scale resolving approaches only one simulation was done, but on a very fine and mostly block-structured numerical mesh to achieve minimal numerical dissipation.

Abstract This article presents a comparative study between two camshafts systems adapted to the single cylinder engine of a Supermileage vehicle in a fuel economy perspective. One system is from a Honda AF70E engine and the other is a new design. The new camshaft system was improved for fuel economy by developing a new camshaft that enhances volumetric efficiency while reducing friction losses. The comparison was made by measuring the efficiency of the engine in the speed range where the engine was used by the Supermileage vehicle and a calculation was made to show which of the configuration is best for the vehicle.

Abstract A fully predictive one-dimensional model of a Common Rail injection apparatus for diesel passenger cars is presented and discussed. The apparatus includes high-pressure pump, high-pressure pipes, injectors, rail and a fuel-metering valve that is used to control the rail pressure level. A methodology for separately assessing the accuracy of the single submodels of the components is developed and proposed. The complete model of the injection system is finally validated by means of a comparison with experimental high-pressure and injected flow-rate time histories. The predictive model is applied to examine the fluid dynamics of the injection system during either steady-state or transient operations. The influence of the pump delivered flow-rate on the rail-pressure time history and on the injection performance is analysed for different energizing times and nominal rail pressure values.

Abstract In order to improve performance and minimize pollutant emissions in gasoline turbocharged direct-injection (GTDi) engines, different injection strategies and technologies are being investigated. The inclusion of exhaust gas recirculation (EGR) and the variation of the start of injection (SOI) are some of these strategies that can influence the air-to-fuel (AF) mixture formation and consequently in the combustion process and pollutant emissions. This paper presents a complete study of the engine performance, pollutant emissions and aftertreatment efficiency that produces the SOI variation with a fixed EGR rate in a 4-cylinder, turbocharged, gasoline direct-injection engine with 2.0 L displacement. The equipment used in this study are TSI-EEPS for particle measurement and HORIBA MEXA 1230-PM for soot measurement being HORIBA MEXA 7100-DEGR with a heated line selector the system employed for regulated gaseous emission measurement and aftertreatment evaluation.

Abstract 36MnVS4 is a new connecting-rod fracture-splitting material. To explore why it has a high fracture- splitting defective index, this article simulated the fracture-splitting process of connecting rods. Comparing 36MnVS4 with C70S6, this article analyzed the stress-strain state of the groove roots, the position of crack initiation, the plastic deformation distribution of the fracture surface, and the splitting force changes in fracture splitting process. Results show that the crack initiation position of the 36MnVS4 connecting rod is relatively more scattered and random, and the crack starting point of the C70S6 connecting rod is more unique. Compared with the C70S6 connecting rod, the 36MnVS4 connecting rod has an earlier crack initiation time and smaller fracture-splitting force. Therefore, the 36MnVS4 has higher gap sensitivity and its fracture surface is more prone to tear.

Abstract Turbocharging can provide a low cost means for increasing the power output and fuel economy of an internal combustion engine. Currently, turbocharging is common in multi-cylinder engines, but due to the inconsistent nature of intake air flow, it is not commonly used in single-cylinder engines. In this article, we propose a novel method for turbocharging single-cylinder, four-stroke engines. Our method adds an air capacitor-an additional volume in series with the intake manifold, between the turbocharger compressor and the engine intake-to buffer the output from the turbocharger compressor and deliver pressurized air during the intake stroke. We analyzed the theoretical feasibility of air capacitor-based turbocharging for a single-cylinder engine, focusing on fill time, optimal volume, density gain, and thermal effects due to adiabatic compression of the intake air.

Abstract Turbocharger compressor maps are used in engine performance modeling and simulation to predict engine air system operating conditions. Errors in compressor map data can result in inaccurate engine performance prediction. A method is described for conditioning compressor map data for use in engine performance simulation, by detecting and replacing suspect data points, and interpolating and extrapolating the map data. The method first characterizes enthalpy rise through the compressor, after removing data points likely influenced by heat transfer from turbine to compressor, using energy transfer coefficient vs. impeller outlet flow coefficient. This is done concurrently with estimating impeller outlet conditions using simplified geometry assumptions and a modified definition for compressor stage reaction.

Abstract Three-cylinder engines were launched, given the increasing demand for improved fuel economy and efficiency along with reduced friction and weight. Unlike four-cylinder engines, these engines are not naturally balanced. So, in order to compete with four-cylinder engines, some methods to solve this inherent weakness, such as balance shaft, mass unbalancing of flywheel and crankshaft pulley, or counterweights configuration (angular orientation and correction amount), have been used. Considering the undesirable characteristics of the balance shaft, such as cost, weight, friction, and noise, as well as dynamically inappropriate mass unbalancing method, this research proposes multi-objective optimization of counterweights to reduce vibrations.

Abstract The rapid utilization of fossil fuels has triggered the finding of alternative renewable fuel that replaces or reduces the consumption by alternative fuels for fueling compression ignition (CI) engines. One such renewable fuel is ethanol which can be manufactured from biomass. The present study details the utilization of an optimum amount of ethanol in CI engine by modifying the operating parameters. It was already published in the previous paper that 45% ethanol can be utilized along with diesel using 10% butanol as cosolvent. This fuel is also meeting the minimum requirement with respect to properties as per ASTM standards. This experimental study was performed to investigate the influence of modifying the engine operating parameters on the performance, combustion, and emission parameters fueled with the blend containing 45% ethanol under various load conditions.

Abstract A comprehensive comparison between a direct acting and an indirect acting piezoelectric injector has been carried out both at the hydraulic rig and at the dynamometer cell. The working principle of these injector typologies is illustrated, and their hydraulic performance has been analyzed and discussed on the basis of experimental data collected at a hydraulic test rig. The injector characteristics, nozzle opening and closure delays, injector leakages, injected flow-rate profiles, injector-to-injector variability in the injected mass, injected volume fluctuations with the dwell time (DT), and minimum DT for fusion-free multiple injections have been compared in order to evaluate the impact of the injector driving system on the injection apparatus performance. The direct acting and indirect acting piezoelectric injectors have been installed on a Euro 5 diesel engine, which has been tested at a dynamometer cell.

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