Browse Topic: Variable compression ratio engines
In the multi-link mechanism of a variable compression ratio engine, the stiffness of the end of the housing increase by adopting the slit structure, this eventually led to an increase in pressure concentrate locally at a certain contact point at the end of the sliding surface of the lower link bearing. As a design solution, this is a report of how to disperses/reduces the generated axial pressure by optimizing the shape of the sliding surface based on FEM/EHD, which are estimated by considering the deformation characteristics of lower link mechanism.
This study introduces the working principle of the two-stage variable compression ratio system, the layout and method of the VCR hydraulic system test. Based on the research and analysis of VCR hydraulic system test, the results shows the average pressure, degree of pressure fluctuation of the VCR conrod supply oil and the temperature of conrod journal are all strongly and positively related to engine speed. The maximum oil pressure fluctuation amplitude at VCR conrod bearing appears at 5500r/min. The temperature at VCR conrod bearing is mainly dominated by the friction between bearing and crankshaft, and its maximum value appears at 6000r/min; Meanwhile, the main contribution of engine load to the temperature is to increase temperature of the whole circle of conrod journal, and also reducing temperature difference of the whole circle. In addition, the state change of VCR hydraulic system under different conditions can reflect the state of engine compression ratio. The results of overall test show that oil pressure fluctuation of the VCR hydraulic system is in normal range, the system has good function and can meet the oil demand of each sub-component under steady and dynamic conditions.
The American Society for Testing and Materials (ASTM) D613 test method involves the use of a variable compression ratio CFR F5 engine to determine the cetane number of diesel fuels for use in compression ignition engines. The CFR F5 remains relatively unchanged since its conception, utilizing a swirl prechamber, mechanical jerk fuel pump, and a 10.3 MPa cracking pressure pintle nozzle mechanical injector. Recent efforts to improve the repeatability of the F5 engine involved the development of prototype engines equipped with electronic fuel injection (EFI) and upgraded high-speed instrumentation. These modifications have demonstrated the capability to improve the ASTM D613 precision limits by at least a factor of two. Parameterization of injection strategy has further optimized the test method, producing cycle-to-cycle variations of ignition delay analogous to modern day compression ignition engines. This study aims to expand on these improvements by identifying and quantifying similarities in ignition characteristics between the EFI F5 and a single-cylinder Caterpillar C9.3B heavy-duty diesel engine. Parametrization studies of injection advance and intake air temperature at fixed compression ratio and a gross indicated load of 2 bar were performed on both platforms with reference fuels at varying cetane number. Apparent heat release analysis was performed for the F5 and C9.3B. Despite the different combustion systems, the F5 and C9.3B have very similar ignition delay characteristics as the fuel and operating conditions are varied. This study validates the F5 engines importance and relevance as the primary cetane rating methodology for diesel fuels used in compression ignition engines.
This paper introduces an internal high ratio gear system with eccentric movement using an involute tooth profile but not the commonly used cycloidal gear profile, and a solution deemed particularly suitable for variable compression ratio actuators. The design challenges of these rotary actuators are discussed, contact ratio values exhibited, and efficiency measurements shown.
Today the whole automotive world is progressively transforming towards the adoption of new alternate, advanced and innovative technologies evolving in ICE and Vehicle technology to meet the stringent emission regulations and future CO2 goals while protecting the environment. May it be Engine downsizing, Down speeding, Cylinder deactivation, VCR, VVT, Dynamic Skip Fire (DSF), Alternate fuels, Alternate materials, Steel pistons, Advanced thermal barrier/coating technology, Electrification or Various degrees of hybridization. The key to achieve better FE or reduction in CO2 emissions is realized by saving every pie of energy spent or reducing the parasitic losses and improving overall engine efficiencies wherever possible. In this paper, an experimental study on the deployment of various energy saving technologies, concepts are exploited on small 2 cylinder common rail BSVI engine for friction reduction and efficiency improvements while moving forward from BSIV to BSVI legislation phase. It has been demonstrated in this experiment that the whole package of friction reduction on an engine saves the engine FHP energy by 15% over the base BSIV engine. The deployment of such technologies not only improves mechanical efficiency of BSVI engine by 5.43 % over the base BSIV engine configuration but also substantial improvement in engine performance and efficiencies with an average benefit of 4.6 % in BSFC over the base engine along with FE benefit when tested on vehicle.
Thermal comfort in the vehicle cabin environment is an important factor for passengers of both internal combustion engines and electric vehicles. Heating, Ventilation and Air Conditioning (HVAC) is a critical system for electric vehicles (EVs) as it is the second most power consumer after electric motor. Novel solutions dedicated to EV, including thermoelectric air conditioning (AC) modules, vapor compression refrigeration (VCR), cycle positive temperature coefficient (PTC) heater as well as heat pumps (HP), are being investigated to maintain a stable and comfortable interior environment under hot and cold weather conditions. At present, the mostly dominated automotive AC systems are those using R134a refrigerant characterized by high global warming potential. Therefore, an innovative and ecofriendly AC system design still must be developed to supply sufficient cooling or heating capacity while minimizing the influence of the AC system on driving ranges and environmental performance. A potential solution is represented by vortex tube-based AC systems. The vortex tube is a fluid dynamic device which is capable to separate an inlet compressed flow in two streams at hot and cold temperature, respectively. The objective of this study is to investigate the feasibility of the use of vortex tube integrated to the transcritical R744 (t-R744) AC system for an electric vehicle. Using a preliminary configuration of a vortex tube device developed for a commercially available mini-EV, the energy analysis of the system under various experimental conditions was performed and its performance parameters under steady state operation were evaluated. Specifically, the Coefficient Of Performance (COP) of the vortex tube transcritical R744 AC system and its influence on the driving range were assessed for different external weather conditions. Finally, this solution is compared with the basic transcritical R744 cycle and with its mostly used modification which considers an internal heat exchanger for the same working conditions of VCR.
In order to meet upcoming emission targets, an increasing number of ships using Liquefied Natural Gas (LNG) as fuel have been put into service. In this context, many shipowners are particularly interested in the dual-fuel (DF) large-engine technology, which enables ships to operate with both gaseous and conventional liquid fuels. The use of different combustion principles in DF engines requires a layout of the base engine with a relatively low compression ratio (CR) for the gas mode to prevent unstable combustion (knocking). However, this layout leads to disadvantages in the Diesel operation mode, which requires a higher CR for optimal fuel efficiency. Therefore, a two-stage variable compression ratio (VCR) system is a technology particularly suitable for DF engines. It allows to reduce fuel costs by approximately 5.5%. This article presents an innovative VCR connecting rod (conrod) design for modern DF engines that adapts the piston position by changing the effective conrod length. The VCR system is developed by the Institute for Combustion Engines of the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University together with Forschungsgesellschaft für Energietechnik und Verbrennungsmotoren (FEV) Europe GmbH. It is equipped with a novel functional principle inside the conrod’s small eye specifically tailored to large engine boundary conditions. The system includes an advanced hydraulic circuit combining the function of a hydraulic freewheel, the oil supply for piston cooling, and a mechanical locking device (LD) for both CRs. In a comprehensive simulation study, the layout and the system behavior of the new hydraulic circuit are presented using a one-dimensional (1D) hydraulic-mechanical simulation model, which was validated in advance with measurement data from a passenger car (PC) engine. The study intends to examine the functional behavior of the VCR system during engine operation. The focus is on the switching process between the two CRs, as well as on the fixed CR operation. The aim is to provide a deeper understanding of the hydraulic-mechanical behavior and to identify special requirements on the system.
In the ongoing competition of powertrain concepts the Internal Combustion Engine (ICE) will also have to demonstrate its potential for increased efficiency [1]. Variable Compression Ratio (VCR) Systems for Internal Combustion Engines (ICE) can make an important contribution to meeting stringent global fuel economy and CO2 standards. Using such technology a CO2 reduction of between 5% and 9% in the World Harmonized Light-Duty Vehicle Test Cycle (WLTC) are achievable, depending on vehicle class, load profile and power rating [2]. This paper provides a detailed description of the measurement approaches that are used during development of the AVL Dual Mode VCSTM and other VCR systems in fired operation. Results obtained from these measurements are typically used to calibrate or verify simulation models, which themselves are an integral part of the development of these systems [3]. The described measurement tasks deal primarily with the analysis of physical phenomena in hydraulically actuated variable-length conrod systems. An interactive development between metrology, design and simulation experts is a key success factor and described here by means of selected measurement tasks. In addition to measurements performed on the moving conrods, multiple methods using stationary sensors were developed for determining the piston position, and therefore the compression ratio. Significant effort is also devoted to the analysis of compression ratio switching events, as the switch times are an especially important aspect of any VCR system.
Lubricating oil from the engines is not utilized properly and these oils are spoiling the land and groundwater significantly. This study is to utilize pyrolised waste engine oil as an additive into diesel, diesel-ethanol, and diesel-butanol blends for the enhancement of essential properties. The study was conducted in two stages: Initially various proportions of pyrolised waste engine oil were blended with diesel, diesel-ethanol (15% bioethanol) and diesel-butanol (20% biobutanol) blends followed by testing the properties to obtain three fuel blends consisting of one from each category (by comparing the base properties with diesel). Properties of these blends were tested and the performance in a compression ignition engine by varying the fuel injection timing 23, 26, and 29 °before top dead centre) was performed. Results of the property testing depicted that the blend containing 10% pyrolised engine oil and 90% diesel, 20% of pyrolised waste engine oil and 80% diesel-bioethanol blend and 15% of pyrolised waste engine oil with diesel-biobutanol blends were possessing closer properties with respect to diesel. Engine test results indicated that 29° before top dead centre of fuel injection timing was found suitable to the engine fuelled with these fuel blends with respect to the performance and emissions. However, the emissions of hydrocarbons and carbon monoxide produced by these blends at low load conditions were found to be marginally higher compared to diesel.
The subject of control of compression and stroke in engines is still a very contemporary research topic, and there is room for research in this matter, as can be asserted from the literature reviewed. In this paper, we report on the systematic methodology followed to perform the synthesis of a variable displacement slider-crank mechanism, needed to convert a non-road small commercial reciprocating single cylinder diesel engine to a variable compression ratio (VCR) engine for academic research purposes. Preliminary dimensions and space trajectories of the projected variable stroke multilink mechanism, constrained by the design of the base engine, were obtained using the coupler curves of Hrones and Nelson’s atlas. A genetic algorithm methodology was implemented to optimize the mechanism performance, as well as to give advantageous compression ratio and displacement behavior, according to both dimensional and kinematic fitness-criteria. A six links Stephenson structure was argued, as the base for a multilink variable stroke slider-crank mechanism, to alter the piston position and stroke variation ranges. With the obtained synthesized mechanism installed in the structure of the base engine, the compression ratio would be varied between 10 and 17.5, at the time that the actual range of piston displacement would be extended in a range between 23 and 38 %. The work conducted is part of a research under work, which pursues to construct the VCR multilink mechanism to install in the available engine.
In the present investigation, oxygenated blend of Kalonji (Nigella sativa) biodiesel-mineral diesel was fueled in a compression ignition engine at variable compression ratios. The Kalonji biodiesel was prepared using a two-stage transesterification process with parameters such as 6:1 methanol to oil molar ratio and 65°C reaction temperature for 120 minutes. The diesel-Kalonji biodiesel blend was used in a 4.4 kW eddy current dynamometer loaded with single-cylinder CI engine. The emission, performance, and combustion characteristics were determined and compared against the base fuel (mineral diesel). Further, 10% of n-butanol, an oxygenated additive, was blended with the diesel-Kalonji biodiesel fuel blend to analysis its impact on emission, performance, and combustion parameters. Moreover, the experimentation was conducted with variable compression ratios (CR 17:1, CR 17.5:1, and CR 18:1) to understand its influence on performance, emission, and combustion aspects.
Depletion of fossil fuel reserves has led the researchers to work on identifying the substitute to be used as a fuel in internal combustion engines. Blending up to 20% biodiesel with mineral diesel is widely accepted among the research community. But, the lack of study on the effect of varying the compression ratios on the performance and emission behaviour of the blended biodiesel fuel led to this present study. This study was carried out on a variable compression ratio direct injection compression ignition engine using pumpkin seed biodiesel as fuel, which was blended at different compositions (20% pumpkin seed biodiesel-diesel and 50% pumpkin seed biodiesel-diesel) and tested at various compression ratios (viz., 17:1, 17.5:1, 18:1). D80PSB20 fuel blend produced higher brake thermal efficiency along with lower brake specific energy consumption. HC, CO, and smoke emissions were lower compared to the mineral diesel. But, oxides of nitrogen was higher due to attainment of higher cylinder temperature. Among all tested fuel blends, D80PSB20 was found to be the best fuel composition and the compression ratio of 18:1 was found to be the best to produce better performance with reduced emissions characteristics.
Natural gas has been used in spark-ignition (SI) engines of natural gas vehicles (NGVs) due to its resource availability and stable price compared to gasoline. It has the potential to reduce carbon monoxide emissions from the SI engines due to its high hydrogen-to-carbon ratio. However, short running distance is an issue of the NGVs. In this work, methodologies to improve the fuel economy of a heavy-duty commercial truck under the Japanese Heavy-Duty Driving Cycle (JE05) is proposed by numerical 1D-CFD modeling. The main objective is a comparative analysis to find an optimal fuel economy under three variable mechanisms, variable valve timing (VVT), variable valve actuation (VVA), and variable compression ratio (VCR). Experimental data are taken from a six-cylinder turbocharged SI engine fueled by city gas 13A. The 9.83 L production engine is a CR11 type with a multi-point injection system operated under a stoichiometric mixture. For minimizing optimal valve strategy selections and engine testing procedures, a one-dimensional engine model is developed in GT-Power software using experimental data and engine specifications provided by a project partner. The model is built using the same theory as of spark-ignition engines. Knock prediction is based on the Shell model, and a spark timing optimization logic is coupled to the model. In-cylinder pressure, rate of heat release, brake mean effective pressure, and maximum brake torque spark ignition timings are well reproduced, as compared with that of 12 experimental operating points under engine speed and load variations. In order to build a baseline brake specific fuel consumption (BSFC) map in the driving cycle, the simulation model is used to generate 51 BSFC points, as proposed in the JE05 cycle under speed-torque changes. From the baseline engine model, the average fuel economy of the heavy-duty natural gas truck is 4.14 km/L. 0.5 % and 2.43% of simulated fuel economy improvements are found when the engine is operated under VVT and VVA mechanisms (fixed lifts), respectively. Significant fuel economy improvement is achieved at about 6.31% under VCR engine operation compared with the baseline engine model.
Spark Ignited (SI) combustions engines in combination with different degrees of hybridization are expected to play a major role in future vehicle propulsion. Due to the combustion principle and the related thermodynamic efficiency, it is especially challenging to meet future CO2 targets. The layout and optimization of the overall system requires novel methods in the development process which feature a seamless transition between real and virtual prototypes. Herein, engine models need to predict the entire engine operating range in steady-state and transient conditions and must respond to all relevant control inputs. In addition, the model must feature true real-time capability. This work presents a holistic and modular modeling framework, which considers all relevant processes in the complex chain of physical effects in SI combustion. The basis is a crank-resolved cylinder model which describes gas exchange and compression to determine the thermodynamic state and turbulence conditions at spark-advance. Ignition and flame front combustion are modeled by a mechanistic, quasi-dimensional combustion model with a detailed consideration of combustion chamber geometry for flame-wall interaction. Cycle-to-cycle variations are imposed in a semi-empirical manner in order to provide realistic boundary conditions for the thermo-chemical knock model. The models are validated against engine measurements for a passenger car sized TGDI engine in a wide range of operating conditions covering the entire engine map. Emphasis is put on comparing pressure and heat release traces, not only for the mean cycle, but for the range of stochastic variations of 100 measured cycles. The validation results confirm a good level of agreement between measured and simulated results. To demonstrate capabilities of the proposed modeling concept, a model-based optimization is performed in a computational study, aiming at an optimization of engine efficiency under knocking constraints. The study examines two motoric measures, namely water injection and variable compression ratio. Finally, the optimized model runs in a transient drivecycle simulation. The test is performed on a HiL system to prove the model’s real-time capability.
Biodiesel and butanol are best-suited liquid fuels to fuel compression ignition engines. This experimental study is to investigate the effects of nano alumina on the performance of a variable compression ratio engine fueled with biodiesel-butanol blends. The experiment was conducted in two stages: Arriving at an optimal blend of biodiesel and butanol from the property testing of the blends followed by fueling the optimal blend containing 50% biodiesel and 50% butanol with nano alumina in four proportions (25, 50, 75, and 100 ppm) variable compression ratio engine. The compression ratio was varied as 16:1, 19:1, and 20.5:1. The compression ratio of the engine was varied by the increase and decrease of the clearance volume as the engine used was a variable compression ratio engine. Nano alumina was blended with biodiesel-butanol blend by ultasonication. The results of the property testing showed that the addition of butanol into biodiesel reduced the kinematic viscosity, cetane number, flash point, energy content, and an increase in oxygen content and heat of vaporization. The addition of nano alumina into biodiesel-butanol blend improved the energy content and cetane number significantly. The significance in the addition of nano alumina is that it is a combustion enhancer and due to its micro explosion and catalytic action, an increase in the rate of oxidation was improved. The engine results were compared with the characteristics of diesel fuel. The engine test results showed that the optimal blend with 100 ppm of nano alumina produced brake thermal efficiency, incylinder peak pressure, peak heat release rate, and ignition delay closer to that of diesel at compression ratio 19:1. However, the increase of compression ratio beyond this produced adverse results. The emissions of oxides of nitrogen and smoke from the engine fueled with the optimal blend and 100 ppm nano alumina were also found closer to that of diesel.
This article serves as a proof-of-concept and feasibility analysis regarding a variable compression ratio (VCR) engine design utilizing an exhaust valve opening during the compression stroke to vary the compression ratio instead of the traditional method of changing the cylinder or piston geometry patented by Ford, Mercedes-Benz, Nissan, Peugeot, Gomecsys, et al. [1]. In this concept, an additional exhaust valve opening was used to reduce the virtual compression ratio of the engine, without geometric changes. A computational fluid dynamics model in ANSYS Forte was used to simulate a single-cylinder, cold flow, four-stroke, direct injection engine cycle. In this model, the engine was simulated at a compression ratio of 10:1. Then, the model was modified to a compression ratio of 17:1. Then, an additional valve opening at the end of the compression stroke was added to the 17:1 high compression model. The valve opening at the end of the compression stroke was used to bleed off a small amount of pressure. This allows an engine to be built for a geometric 17:1 compression ratio (longer cylinder) while also having the ability to “act” as a 10:1 compression ratio engine due to the valve pressure release. By manipulating the timing of the valve opening, the engine would operate with a compression ratio anywhere between 10:1 and 17:1 depending on the load/speed knock limit. The additional valve opening profile was developed from the initial valve opening during the exhaust stroke. The timing of the additional valve opening was manipulated over multiple simulation iterations to finally achieve approximately the same maximum cylinder pressure as the first simulation trial (Test 11 CR17b). Opening a valve twice in one cycle ideally uses direct injection and camless valve operation. Available valve actuator technology was compared to the required valve actuation speed for this design and was determined to be feasible. In addition, fuel injection timing was investigated regarding near-top dead center (TDC) injection. Fuel must be directly injected after the exhaust valve closes during the compression stroke to avoid fuel loss through the exhaust manifold. This late fuel injection was determined to be feasible based on previous injection-timing studies [12].
This work involves a with comparative study of smoke emission reduction methods of a compression ignition engine fueled with neat Waste Cooking Oil (WCO). The test engine chosen for this study is an agricultural based single cylinder, with a variable compression ratio, which is water cooled and is of the direct injection compression ignition engine type. Initially the test engine was tested using with neat diesel and WCO using various load conditions with three different compression ratios, i.e., 16.5, 17.5 and 18 for its performance, emission and combustion behaviours respectively. Results revealed that, both diesel and neat WCO experienced higher Brake Thermal Efficiency (BTE) with increased compression ratio. Except for smoke emission, all other carbon based emissions of neat WCO was found to reduce with increased compression ratio. In view of the above identified problems, a fuel and engine level modification was carried out introduce to the best practice of operating the engine with least smoke emission. Emulsion and injection timings were chosen as two parameters, and their influence on the smoke emission of the engine operated with neat WCO was studied. Standard injection timing (i.e. 23oBTDC) of the engine was increased by a maximum of four degrees at an interval of 2o crank angle. Subsequently, an emulsion was made with neat WCO and tested in the engine for smoke emission. Comparison of the results of smoke emission obtained after implementing the two different control methodologies, showed a higher percentage of smoke emission reduction (i.e. 25%) with respect to emulsified WCO when compared to the advancement of injection timing. Emulsification method also obtained the benefits of reduced oxides of nitrogen emission of neat WCO. However, the BTE was reduced marginally (i.e. 8%) when emulsified fuels were used which improved with advancement of injection timing. Hence, this work suggests that emulsification techniques will be a better choice for operating the engine when the reduction of smoke emission is considered as the prime objective whereas for the optimized operation, it is suggested that advancement of injection timing be used as a correct choice for operating the engine with neat WCO.
The competitiveness within the automotive sector increases constantly. Research institutes, universities and manufacturers are commonly trying to discover the new trends and to develop novel technologies. Nevertheless, it is important to understand if a certain technology is worth researching. In order to do that, a state of the art survey is necessary which is usually divided in two main groups: Literature Information and Market Analysis. The literature information regards papers, congress proceedings, books, among other types of formal publication. The market analysis is responsible to gather information within the manufacturers press releases, websites and events, for example. Even though, depending on the technology, those two topics are not enough to reveal the importance of a given technology. Therefore, it is necessary to search the patents database, where it is possible to find the development status of a device. However, a patent survey it is not trivial and some methodology is needed. This papers aims on proposing a proper methodology for patent survey focused on automotive mechanisms such as gear trains, suspensions, steering and engines. The methodology it is explained step by step and a brief overview about patents is given. At the end a case study regarding the Variable Compression Ratio engines is given. This proper methodology for patent survey allowed the researchers to propose an enhanced classification for the VCR topic, to help defining design requirements and to understand the potential for innovation within the desired topic.
The Automobile industry is under great stress due to greenhouse gas emissions and health impacts of pollutants. The rapid decrease of fossil fuels has promoted the development of engine designs having higher fuel economy. At the same time, these designs keep the stringent emission standards in check without sacrificing brake power. Variable Compression Ratio (VCR) is one such measure. This work reviews the technological advancements in the design of a VCR engine. VCR engines can minimize possible risks of irregular combustion while optimizing Brake specific fuel consumption towards higher power and torque. An increase in fuel economy is seen for VCR naturally aspirated engines when coupled with downsizing. In addition to this, emissions of carbon dioxide decreases due to effective utilization of fuel at high loads. Since the first VCR design, there have been various modifications and improvements in VCR engine design. This paper describes the various techniques by which VCR is being implemented and provides a comparative study of original and modified technology on the basis of efficiency, engine friction, specific fuel consumption, engine rigidity and piston kinematics. The paper then reviews various historical designs which use the above mentioned techniques patented by Ford, Mercedes Benz, Nissan, Peugeot and Gomecsys and discusses their advantages. Lastly the paper explains the design, working and advantage of three VCR designs that are closer to production.
MCE-5 DEVELOPMENT has been developing its variable compression ratio engine (VCRi) for over a decade aiming at reducing fuel consumption and pollutant emissions. In order to transmit power from the piston (combustion) to the crankshaft, the MCE-5 VCRi technology is based on three innovative components: a gear wheel and two racks. This gear mechanism ensures a very low friction compared to other continuous VCR solutions based on bearings. However, this transmission is used in nonstandard conditions: the direction of rotation is reversed repeatedly, and the parts are submitted to high and rapidly varying loads. To avoid interferences and alteration caused by high contact pressure at high load, and ensure a regular transmission at low load, the profile of the teeth is carefully considered. A crowning shape is placed on the teeth in the direction of the gear axis, and a correction is applied to the tooth active profiles in the area of tooth roots and tooth tips. A Design of Experiment (DOE) is realized on a light Finite Element 2D model in order to highlight the influence of the parameters of the correction on the maximum stress and the contact pressure on the teeth, and on the speed ratio between the gear and racks. A refined Finite Element 3D model is developed in order to obtain more accurate results concerning the contact pressure and the stress on the teeth, and to take into account the crowning shape. Endurance experiments were conducted on engine test benches before and after optimization of the tooth profile. Observations of the teeth show the benefice of this method, with a suppression of the wear and pitting on the surface contact.
The continuous growth of population and development of industries give rise to massive increase in the global energy demand in recent years. Therefore present work investigated the combustion and emission characteristics of an unmodified four stroke single cylinder variable compression ratio diesel engine utilizing isopropyl alcohol (2-propanol)-diethyl ether blends with diesel. The different fuel samples were prepared using 10% isopropyl, alcohol 5% diethyl ether by volume (IPD15), 15% isopropyl alcohol, 5% diethyl ether by volume (IPD20) and 20% isopropyl alcohol 5% diethyl ether by volume (IPD25) with neat standard diesel. All experiment tests were performed with at variable compression ratio 17 and 18 at different load conditions. The effect of blends and compression ratio on combustion parameters viz. peak cylinder pressure and rate of heat release along with exhaust emissions CO, CO2, HC and NOx, were investigated. The results of the experiment has been investigated and compared with standard diesel and results exhibited the higher peak cylinder pressure and heat release for IPD15 and IPD20 than that of IPD25 at both compression ratio 17 and 18. However exhaust emissions strongly depend on engine operating conditions and proportions of isopropyl alcohol-diethyl ether blends though It has been observed that increase in concentration of isopropyl alcohol in isopropyl alcohol (2-propanol)-diethyl ether blends reduces NOx emissions, while increasing CO and HC emissions at compression ratio 18.On the basis of combustion and emission studies of present investigation IPD15 and IPD20 may be used as suitable alternative fuels for diesel engines without major modification in engine compounds.
The aim of present work is to investigate the performance and emission characteristics of a four stroke, single cylinder variable compression ratio engine fuelled with blends of diethyl ether, linseed oil methyl ester and neat diesel. In the experiment content of diethyl ether kept constant as 5% by volume for all fuel samples whereas linseed methyl ester biodiesel content was varied as 10%, 15% and 20% by volume. The different fuel samples DLD15, DLD20 and DLD25 with neat standard diesel. Experiment tests were performed with engine speed 1500 rpm and variable compression ratio 16, 17 and 18 at different load conditions. The effect of blends and compression ratio on different performance parameters viz. brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), and exhaust gas temperature along with emissions CO, CO2, HC and NOx, were investigated. Results showed that DLD20 and DLD25 exhibited the prominent engine performance and exhaust emissions compared to diesel fuel.
Replacing the conventional fossil fuel totally or partially with alcohols or ethers in spark-ignition (SI) engine is a promising way to reduce pollutant emissions. A large number of studies on alcohol-containing blends in SI engines could be found in the literature. Nonetheless, investigations of ether-containing blends are by far much less numerous, especially for modern boosted engines. Blending with ether compounds might change the burning rate at high pressure, which consequently changes the anti-knock properties of these fuels and leads to a deterioration in the vehicle drivability. This work reports experiments carried out in two one-cylinder engines: one is a naturally aspirated, variable compression ratio engine, and the other is a strongly charged optical engine. Three fuels with different RON and MON numbers were tested: Iso-octane, a blend Ethyl Tert Butyl Ether (ETBE) with a primary reference fuel, and a commercial gasoline fuel containing 5% by volume of ethanol (E05). The experimental results show a significant difference of knock boundaries of three fuels in the boosted engine at the initial, i.e. equivalent of the intake manifold, pressure of 1.6bar, and almost similar knock boundaries under different compression ratios in the naturally aspirated engine. The fuel sensitivity upon the knock boundary of oxygenated blends was identified in order to compare the fuels' performance in different engines. The burning rate was determined at the same compression ratio for the two engines from the high speed flame imaging and a reverse-thermodynamic analysis, in order to clarify the effects of the burning rate on the anti-knock behaviour.
In this work, optimization of various parameters, such as injection timing, compression ratio (CR) and amount of ultra-cooled exhaust gas recirculation (EGR) has been done for a variable compression ratio engine. The CR can be adjusted dynamically by changing the clearance volume through a tilting cylinder block arrangement. An EGR system, suitable for achieving ultra-cooled as well as treated EGR and large range of flow rates, has been implemented. Taguchi analysis was employed to carry out minimum number of experimental runs and still get the essence of large number of test cases. Effect of these parameters on engine performance and exhaust emissions has also been studied with the help of signal to noise (SN) ratio analysis. Flatter and wider HRR traces were observed in previous work of Brijesh et al., indicating a low temperature combustion (LTC) mode for the runs having optimized input parameters. Simultaneous reduction of NOx and PM were achieved for runs with optimized parameters in the first stage, but HC and CO emissions were slightly higher compared to the base run. During the current study, second stage of optimization has been carried out for further reduction in emissions with improved performance. Combination of input parameters selected for run 4 of second stage optimization, i.e., -15 CAD aTDC injection timing, 18 CR, 220 bar injection pressure and 25% ultra-cooled EGR seems to be the optimum set of operating parameters for this engine. LTC mode has been achieved with these optimum operating parameters. Brake thermal efficiency was also improved by around 12% compared to that with the base operating parameters. The optimization method indicates that LTC achieved by the combination of retarded injection timings and moderate rate of ultra-cooled EGR, also provides better efficiency even with low injection pressure (~ 220 bar). Increase in HC and CO emissions had been reported as a major issue with LTC in various literatures. But in the present work, reduction in CO and only a slight increase in HC emissions were observed even with LTC mode of combustion. It was mainly possible due to moderate use of ultra-cooled EGR. Compared to conventional EGR, lower amounts of ultra-cooled EGR were sufficient to achieve similar reduction in NOx and PM with reduced HC, CO. Use of ultra-cooled EGR is beneficial in achieving LTC even at higher load conditions. Additionally, decrease in pressure rise rate (PRR) and hence engine noise was also observed.
Several studies have been performed to investigate the effects of using hydrogen in spark ignition (SI) engines. One general conclusion that emerged was that stoichiometric operation of premixed charge hydrogen engines features increased losses compared to other fuels such as methane. Most studies attribute this higher loss to increased rates of heat transfer from the working fluid to the combustion chamber walls. Indeed, heat flux measurements during combustion and expansion recorded much higher values for hydrogen compared to methane stoichiometric operation. With regard to fluid properties, using the same net heat release equation as for gasoline engines results in an over prediction of heat losses to the combustion chamber walls. Also, the variation of specific heats ratio greatly influences calculated values for the rate of heat release. Therefore, a more detailed analysis of heat losses is required when comparing hydrogen to other fuels. This study addresses an issue that is generally overlooked when performing in-cylinder pressure trace analysis, namely the variation of molar mass of the working fluid during combustion. Of course, this variation also influences one major parameter, the specific heat of the working fluid. A one zone thermodynamic model was used for evaluating a first law analysis of the closed valves part of the four stroke cycle. All components were considered as ideal gases, with varying specific heat. Given that combustion is the most complex process of the thermodynamic cycle, fluid composition was taken as constant during compression and expansion. Properties during combustion were calculated using the fired - motored pressure ratio to evaluate burned mass fraction, and fluid temperature was considered as a bulk value, uniform throughout the combustion chamber. Several assumptions, such as complete combustion were also used so that the influence of molar variation could be easily identified. Two sets of measurements were compared, one for hydrogen and one for methane, both recorded during stoichiometric operation. The analysis of these measurements performed on a constant speed, variable compression ratio engine found that hydrogen is at a disadvantage compared to the fossil fuel that features no molar variation during combustion, as more heat was needed to produce the same indicated work. Two more sets of measurements recorded during lean hydrogen fueling were investigated in order to evaluate overall heat losses compared to stoichiometric operation. A new equation is proposed for in-cylinder pressure trace analysis, so that the effect of working fluid molecular weight variation is not overlooked.
The Atkinson cycle engine is basically an engine permitting the strokes to be different lengths for improved light loads fuel economies. Variable compression ratio is the technology to adjust internal combustion engine cylinder compression ratio to increase fuel efficiency while under varying loads. The paper presents a new design of a variable compression ratio engine that also permits an expansion ratio that may differ from the compression ratio therefore generating an Atkinson cycle effect. The stroke ratio and the ratio of maximum to minimum in-cylinder volumes may change with load and speed to provide the best fuel conversion efficiency. The variable ratio of maximum to minimum in-cylinder volumes also improves the full load power output of the engine. Results of performance simulations are proposed for a gasoline engine 2 Litres, in-line four, turbocharged and direct injection showings significant fuel savings during light and medium loads operation as well as improvement of full load output and fuel efficiency.
Variable compression ratio is the technology to adjust internal combustion engine cylinder compression ratio to increase fuel efficiency while under varying loads. The paper presents a new design of a variable compression ratio engine that allows for the volume above the piston at Top Dead Centre (TDC) to be changed. A modeling study is then performed using the WAVE engine performance simulation code for a naturally aspirated gasoline V8 engine. The modeling study shows significant improvements of fuel economy over the full range of loads and especially during light loads operation as well as an improvement of top power and torque outputs. Adjusting the Compression Ratio CR from the low speed wide open throttle knock limited value of CR=10:1 to a variable CR=10:1 to 15:1 for better or about same margin to knock over the full range of engine speeds and loads, maximum torque, power and brake engine thermal efficiency are increased by 5%, 12.5% and 4.5% respectively, while operating at 1 bar Brake Mean Effective Pressure (BMEP) and 2 bar BMEP the brake thermal engine efficiency is up to 10% better.
Experimental investigations are carried out to establish the stability characteristics of various diesel-ethanol blends with the use of neat castor oil and its methyl esters as additive. After a series of analysis, it is found that the blended fuel is stable with 10% castor oil up to E10 blends and with castor oil methyl esters; the stability is maintained up to E25. The performance and emission tests are carried out using the stable fuel blends on a computerised variable compression ratio engine and compared with neat diesel. The tests revealed that castor oil and its methyl esters can be used as an additive to prevent phase separation and the engine performance and emission reduction could be improved significantly by using the stable diesel-castor oil-ethanol and Diesel-COME-ethanol blends with suitable compression ratio.
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