Knock occurs when a rapid release of energy in the remaining unburned mixture causesa rapid increase in local pressures. In hydrogen-diesel engines, knocking will take place when the fraction of total energy contained in hydrogen is more than 16% and the engine will not work in a stable condition if 100% hydrogen is used. A combination of hydrogen and diethyl ether (DEE) produced severe knock on 100% loadand higher hydrogen content leads to a higherprobability of knock onset. Knocking phenomena can be traced from the in-cylinder pressure variations, observing the instantaneous local pressure rise. The graph formed depends on the knocking frequency: the higher the frequency, the more severe the knock .However, there is no concrete mechanism in the literature describing the knocking phenomenon in HCCIengines and the methods to control it. In SI engines, it is quite easy to control knock: car manufacturers usually install knock and oxygen sensors in the engine. If the mixture is prone to generate knock, they will adjust the spark timing accordingly. But in HCCIengines, there is no spark to control such situations andit all heavily depends on the right mixtures and conditions.
Knocking in SI engines is a phenomenon where the unburned mixture in the compressed gas ignites before it is reached by the propagating flame front (Stiesch 2003). Knock is physically detected when the engine vibrates excessively and a pinging sound can be heard outside as a result of the combustion activity. It causes loss of power and, if not controlled, knocking could lead to severe engine damage and shorten its life. Knocking can occur in any reciprocating engine. HCCIengines are prone to knock since they are controlled by chemical kinetics and there is no fixed mechanism to control knock in them. Knocking phenomena limit the load range of an HCCI engine: high load operations can easily initiate knock, so upper load limits have to be applied (Yap et al. 2006). In all engines, generally knocking occurs when the combustion starts before the piston reaches TDC, while misfire is when combustion commences after TDC. Knocking and misfire are two different behaviours which must be avoided in engine operation as both of them can contribute to deterioration of engine performance (Andreae et al. 2007; Jun, Ishii & Iida 2003; Kong & Reitz 2003; Nathan, Mallikarjuna & Ramesh 2010; Yelvington & Green 2003).
Homogeneous charge compression ignition (HCCI) engines have been an active research area recently due to their advantages in reducing emissions levels. Regulatory bodies, such as those in Europe, the United States and Japan, are imposing stringent vehicle emissions quality standards. Most automotive manufacturers are moving towards fuel efficient vehicles by developing hybrid (combination of two or more power sources) vehicles or improving on any conventional engine technology that can reduce emissions levels. Hybrid vehicles are receiving increasing attention from most manufacturers because they offer advantages including reduced emissions and providing good mileage per fuel tank. The HCCI engine has the potential to replace the current conventional engine used in hybrid vehicles, which can reduce the emissions levels further.
Table 2 shows that the fuel cell has the highest electric efficiency (40%), followed closely by the diesel engine. HCCIengines have much lower specific power (or brake mean effective pressure, BMEP) than other engines due to the high level of dilution and the high intake temperature. Lower BMEP results in bigger displacement for a given power output and therefore higher capital cost. Spark-ignited engines and diesel engines have reasonably small displacements and capital costs due to their high BMEP 3 . Fuel
stoichiometric (Ө=1) diffusion flame. This rich combustion may cause soot production depending upon the soot formation tendency of the fuel and the Ө-T distribution during the pre-mixed combustion period. Once the combustion of the fuel prepared to flammability limits during the ignition delay period is over, the rate of combustion further depends on a mixing controlled basis. In the conventional diesel combustion, thermal NOX is produced when the local in- cylinder temperatures are in excess of 1800-2000 K and there is enough oxygen available. Considering approximately adiabatic combustion, these combustion regions fall in soot and NOx regions respectively, resulting in high levels of emissions. SI combustion also generates significant amount of NOx emissions, but they are removed by modern three-way catalysts. As it is clear from Fig. 2 that the HCCI combustion falls outside the soot and NOx islands. In HCCI combustion as the flame temperatures are considerably lower than the conventional diesel combustion due to lean or diluted mixture, the NOx emissions are low.
In some cases, the validation results are very good, where the red points are just located at the centre of purple zone, such as cases 1, 2, 3, 4 and 6. For example, in case 1, the red points are evenly distributed in the purple zones of ISFC and ISHC surfaces. However, some of the cases do not show such good results, e.g. for cases 7 and 8. For case 8, it looks like the optimizer cannot find the best solution for each target optimization objective and only found some compromised points in the blue areas. This is mainly due to the simulation errors of the HCCI engine model. Another possible reason is that 40 EA loops are not enough to optimize the engine for achieving the best performance for this case. This case has a relatively wider surface than others which implies that there are more potential parameter settings for this case.
HCCI combustion process is totally different from the SI and CI engine because of no flame propagation. Chemical kinetic has a dominating role in HCCI combustion. This new concepts of engine has higher thermal efficiency, lower emissions and lower fuel consumption. HCCIengines are cheaper than conventional engine because of their simple construction. HCCI engine is an alternative strategy when CI engines cannot achieve future NOx and PM standards. Difficulties associated with the HCCI engine like combustion phase control, cold start, homogenous charge and extending range of operation has to be overcome for the successful operation of HCCI engine.
Homogenous Charge Compression Ignition (HCCI) engines hold promise of high fuel efficiency and low emission levels for future green vehicles. But in contrast to gasoline and diesel engines, HCCIengines suffer from lack of having direct means to initiate combustion. A combustion timing controller with robust tracking performance is the key requirement to leverage HCCI application in production vehicles. In this paper, a two-state control-oriented model is developed to predict HCCI combustion timing for a range of engine operation. The experimental validation of the model confirms the accuracy of the model for HCCI control applications. An optimal integral state feedback controller is designed to control the combustion timing by modulating the ratio of two fuels. Optimization methods are used in order to determine the controller’s parameters. The results demonstrate the designed controller can reach optimal combustion timing within about two engine cycles, while showing good robustness to physical disturbances.
Most of the investigations in conventional engines are finding new strategies for reduction of emissions and enhancement of their performance [1, 2]. It is well known that Homogeneous Charge Compression Ignition (HCCI) engines have benefits of both Otto and diesel cycles. Possibility of having ultra lean mixture and lower combustion temperature together with no throttling losses could give a great advantage for reduced Nitrogen Oxides (NOx) and particulate matter emissions while increasing the efficiency compared with conventional internal combustion engines . A major advantage of HCCI combustion is its flexibility to work with a variety of fuels. Reduction in availability and increased price of fossil fuels on one hand, and more strict legislations for engine emission levels result in increased interest in application of HCCIengines.
It is expected that the vehicle density will increase significantly in coming future, therefore more strict emission regulations has to come. It is very important to make the compulsory use of the control techniques in the vehicles to meet the emission standards. The future study to be focused is on the development of alternative diesel emission control techniques based on the future Indian emission standards. Many challenges remain before HCCIengines are practical. HCCI combustion has several main difficulties. These difficulties include ―control of combustion timing,‖ ―limited power output,‖ ―homogenous mixture preparation,‖ ―high unburned Hydrocarbon (HC) and carbon monoxide (CO) emissions,‖ and ―weak cold-start capability‖ HC and CO emissions of HCCI engine are relatively higher in comparison with those of diesel engines . Some potential exists to mitigate these emissions at high load by using direct in-cylinder fuel injection to achieve appropriate partial-charge stratification. However, in most cases, controlling HC and CO emissions from HCCIengines will require exhaust emission control devices where fuel optimization was not used. Catalyst technology for HC and CO removal is well understood and has been standard equipment on automobiles for many years. However, the cooler exhaust temperatures of HCCIengines may increase catalyst light-off time and decrease average effectiveness. As a result, meeting future emission standards for HC and CO will likely require further development of oxidation catalysts for low-temperature exhaust steams. However, HC and CO emission control devices are simpler, more durable, and less dependent on scarce, expensive precious metals than are and PM emission control devices. Thus, simultaneous chemical oxidation of HC and CO in an HCCI engine is much easier than simultaneous chemical reduction of and oxidation of PM in a Compression-Ignition Direct-Injection (CIDI) engine.
After solving the compression ratio problem we must note that normal petrol cannot directly be used for HCCI. HCCI engine are likely to knock since they are controled by chemical kinetics and there is no fixed mechanism to check knock in them. Knocking phenomena restricts the load range of an HCCI engine: upper load operations can easily initiate knock, so high load limits have to be applied. In all engines, knocking occurs when the combustion starts before the piston reaches TDC, while misfire is when combuustion commences after TDC. Knocking and misfire are two different behaviours which must be avoided in engine operation as both of them can contribute to deterioratin of engine performance . If HCCIengines operate on hydrogen–diesel fuels, knocking is expected to occur when high amount of hydrogen is added. Knocing will take place if the hydrogen content is more than 16% of the energy ratio it was necessary to use hydrogen with mass fraction less than 15% to achieve stable combustion. VIII. CONSTRUCTION OF AIR PRE HEATER
Homogeneous Charge Compression Ignition (HCCI) is a new combustion technology that may develop as an alternative to diesel engines with high efficiency and low NOx and particulate matter emissions. HCCIengines can operate on gasoline, diesel fuel and most alternative fuels. The Homogenous Charge Compression Ignition (HCCI) is a promising new engine technology that combines elements of the diesel and gasoline engine operating cycles. Like an SI engine, the charge is well mixed which minimizes particulate emissions, and like a CIDI engine it is compression ignited and has no throttling losses, which leads to high efficiency. However, unlike either of these conventional engines, combustion occurs simultaneously throughout the cylinder volume rather than in a flame front. With the advantages there are some mechanical limitations to the operation of the HCCI engine. The main drawback of HCCI is the absence of direct combustion timing control. This seminar report reviews the technology involved in HCCI engine, and its merits, demerits and applications. The recent developments in HCCI engine are also discussed.
The Homogeneous charge compression ignition (HCCI) combustion is an alternative to current engine combustion systems and research in HCCI is being carried out to use it as a method to reduce emissions. In this research performance and emission characteristics of HCCI combustion has been investigated experimentally. Experiment was performed in modified single cylinder diesel engine which has conventional mode of starting and then followed by HCCI mode. The basic requirement of the HCCIengines is homogeneous charge preparation, which is attained by using port fuel injection strategy. An external device was used for fuel vaporization and mixture formation.
In most of the time, people are looking for manufacturing new meshing for exploring the unreachable heights. Now we are trying to make our space dreams come true. To make it real, we need an ultra-modern engine for flying our air craft in to the unending space. But unfortunately, our conventional rocket engines and rocket are not capable to solve our expatiations. So, we need a best, smart, reusable, green and sophisticated engine for levitating our air plane to the space.
Web surfing for various purposes has become a habit of humans. Searching for information from the Internet today has been made easier by the widely available search engines. However, there are many search engines and their number is increasing. It is of considerable importance for the designer to develop quality search engines and for the users to select the most appropriate ones for their use. The Information quality linked through these searches is quite irregular. There are fair chances that the retrieved results are irreverent and belong to an unreliable source. In fact, most search engines are developed mainly for better technical performance and there could be a lack of quality attributes from the customers’ perspective. In this paper, we first provide a brief review of the most commonly used search engines, with the focus on existing comparative studies of the search engines. The paper also includes a survey conducted of 137 respondents where the identified user expectations will be of great help not only to the designers for improving the search engines, but also to the users for selecting suitable ones. The objective behind this study was also to find the reason behind poor precision and recall of so many available search engines. The study finally aims to enhance user search experience.
The stack forms the heart of the thermoacoustic engines. The most common stack geometries have a characteristic constant cross-section channel along the direction of the flow. In standing-wave systems is beneficial to have pores with a radius of one or more thermal penetration depths, it is ܰ ͳ . This is necessary to create the optimal phasing between pressure and velocity and create an optimal heat-shutting effect. The highest acoustic power is obtained if ܰ ̱ͳ , the Lautrec number is defined as :
Fifteen different thermal barrier coatings ceramic powders have been evaluated. Using advanced modelling techniques. This study aimed to predict engine conditions and performance. This has been done with thick coatings rather thin considered for diesel or SI engines. In this study powder characteristics and and chemistry have been considered. The authors have also considered bond coat composition, coating design, microstructure and thickness effect on properties, durability and reliability. In this study spray parameters have been optimized for each powder. Coatings have been evaluated for each powder. Coatings have been evaluated for their performance especially with regard to fatigue failure and aging behaviour.
In Europe, the basic raw material for the pro- duction of biofuels is rapeseed. Basic biofuel used to power diesel engines are esters of fatty acids (FAME, FAEE). Esters of pure vegetable oils have good solubility in diesel fuel. This fea- ture allows to create commercial mixtures of biofuels such as B10, B20. Due to high viscos- ity, low freezing point, water content and organic acids using pure rapeseed oil is not desirable. It may lead to seizure or damage of injection equip- ment and engine. The fuel in the supply system is also the only lubricating medium. The amount of hydrocarbons containing carboxyl group deter- mines the lubricity of the fuel, what makes them chemisorbed on a clean metal surface . Ethyl and methyl esters differ in products of incomplete combustion. In the process of incomplete combus- tion of the methyl esters, toxic substances, such as formaldehyde and radicals, are exuded, which do not occur in the case of incomplete combustion of the ethyl esters . Exhaust gasses of diesel engines powered by RME contain three times more free methyl radicals than exhaust gasses of