A Review Study on Bio-Diesel Droplet Ignition

A Review Study on Bio-Diesel Droplet Ignition

V. D. Sonara1 and Dr. Pravin P. Rathod2,

PG Student1, Associate Professor2 Mechanical Engineering Department

Government Engineering College, BHUJ-37001

ABSTACT

Biodiesel is one of the part solutions in alleviating the worlds dependence on fossil fuels due to the rapid depletion of non-renewable petroleum resources. Biodiesel is an alternative fuel produced from renewable resources with potential to substantially reduce emission associated with petroleum diesel usage.

Combustion and Ignition analysis of Biodiesel and its blends with diesel gives insight into it. Diesel droplet ignition reveals stages of combustion and droplet vaporization at given condition. Further, investigation has proved the effect of Reynolds number on vaporization of droplet at various conditions. Few of the researchers have studied the different parameter(such as Cetane number engine power, economy, engine torque, brake specific fuel consumption ,brake thermal efficiency, exhaust gas temperature) and also find reduction in emission(PM,CO,HC) and increased NO formation. All the fuel tested adheres to the relationship, more or less with droplet complicated size variation and with droplet surface area d2 v/s time.

Combustion characteristics as well as engine performance are measured for different biodiesel diesel blends. It has been shown that B50 (50% of biodiesel in a mixture of biodiesel and diesel fuel) gives the highest peak pressure at 1750 rpm, while B10 gives the highest peak pressure at low speed, 1000 rpm. B50 shows upper brake torque, while B0 shows the highest volumetric efciency. B50 shows also, the highest BSFC by about (12.525%) compared with diesel fuel. B10 gives the highest brake thermal efciency. B50 to B30 show nearly the lowest CO concentration, besides CO concentration is the highest at both idle and high running speeds. Exhaust temperature and NO are maximum for B50. Delay period is measured and correlated for different blends. The delay period is found to be decreased with the increase of cylinder pressure, temperature and equivalence ratio.

Key words: Ignition delay; Diesel engine; Bio-Diesel, Combustion

1. Introduction

   The resources of petroleum as fuel are dwindling day by day and increasing demand of fuels, as well as increasingly stringent regulations, pose a challenge to science and technology. With the commercialization of bioenergy, it has provided an effective way to ght against the problem of petroleum scarce and the inuence on environment. Bio- Diesel, as an alternative fuel of diesel, is described as fatty acid methyl or ethyl esters from vegetable oils or animal fats. It is renewable, biodegradable and oxygenated. Although many researches pointed out that it might help to reduce greenhouse gas emissions, promote sustainable rural development, and improve income distribution, there still exist some resistances for using it. The primary cause is a lack of new knowledge about the inuence of Bio-Diesel on diesel engines. For example, the reduce of engine power for Bio-Diesel, as well as the increase of fuel consumption, is not as much as anticipated; the early research conclusions have been kept in many peoples mind, that is, it is more prone to oxidation for Bio-Diesel which may result in insoluble

   gums and sediments that can plug fuel lter, and thus it will affect engine durability [13].

2. Bio-Diesel

This section provides a basic overview of Bio-Diesel. Technical details about many aspects of Bio-Diesel are provided in Sections.

1.1.1Bio-Diesel Basics

Bio-Diesel is a diesel replacement fuel for use in CI engines. Renewable energy source such as natural gas, biogas, vegetable (green) biofuels are recently gained much scientic efforts to be produced in economical, available, safe and environment friendly nature. Bio-Diesel as an alternative fuel derived from vegetable (green) oil or animal fats are oxygenated, biodegradable, on-toxic and environmentally safe. It consists of alkyl monoester of fatty acids from tri-acyglycerols. Bio-Diesel s are classied into two categories; namely edible and non-edible oils. Edible oils are such that sunower, corn, rapeseed, palm, soybean and waste vegetable oils. The non-edible oils are such that Jatropha, Jojoba, Karanja, Polanga oils and likes [13].

Because plants produce oils from sunlight and air, and can do so year after year on cropland, these oils are renewable. Animal fats are produced when the animal consumes plants or animals, and these too are renewable. Used cooking oils are mostly plant based, but may also contain animal fats. Used cooking oils are both recycled and renewable. The Bio-Diesel manufacturing process converts oils and fats into chemicals called long-chain mono alkyl esters, or Bio-Diesel. These chemicals are also referred to as fatty acid methyl esters (FAME) and the process is referred to as trans esterification. Roughly speaking, 100 pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide [NaOH] or potassium hydroxide [KOH]) to form 100 pounds of Bio-Diesel and 10 pounds of glycerin. Glycerin is a sugar, and is a co product of the Bio-Diesel process.

1. Diesel Combustion

   While diesel engines are well known, an in-depth understanding of how a diesel engine works is required to understand this topic. Some aspects are introduced here, but for a more detailed description see the long report. The diesel engine is a form of compression ignition, internal combustion engine. First built by Rudolph Diesel in 1894, the original version ran on peanut oil. Diesels quickly evolved to use petroleum based diesel, which burnt more completely with less soot than vegetable oils. Diesels use some of the heavier fractions from distillation of crude oil and the fuel is generally composed of blends of C 11 to C hydrocarbon chains.

2. Heat Release Rate

   One of the most common measures used in analyzing diesel combustion and ignition delay is the heat release rate (HRR), due to the large amount of information gained from it and the simple pressure diagnostics required to determine it. An example of a typical HRR plot is shown in Fig.2.1, showing the three major zones commonly associated with DI diesel engines. After fuel injection begins and before combustion, the fuel takes a short time to ignite. During this ignition delay fuel vaporizes and mixes with air, after

   igniting this mixture burns rapidly causing what is known as the premixed burn spike[17]. Once this prepared mixture has combusted, the burning rate is controlled by mixing of the fuel jet and fresh air. This period is called the diffusion ame, and lasts until the injector closes.

   Fig.2.1 typical HRR plot [17]

3. Ignition delay

   Ignition delay is commonly dened as the time between the start of injection (SOI) and the start of combustion (SOC). These two points in the engine cycle are rather arbitrarily dened. For example, experimental measurements for the start of injection often use Hall Effect transducers to measure needle lift, or monitor fuel rail pressure for a drop corresponding with injection.

   Fig. 2.2: Illustration of the eect of ignition delay on the HRR [17]

   Start of combustion (SOC) is also rather arbitrary with many dening it as the rst moment of positive heat release, while researchers with visual access usually use the start of luminous ame. Ignition delay is an important tuning parameter. If a fuel i injected and then undergoes a delay before ignition, the fuel evaporates and mixes with the air charge in the cylinder. After ignition, this premixed charge burns very rapidly, producing high pressures. The effect of rapid burning can easily be seen in heat release rate diagrams, where the later the premixed combustion peak occurs the larger it is, as illustrated in Fig.2.2 This rapid combustion produces regions of high temperature which cause large NOx emissions through the thermal NO mechanism and also produce large peak pressures. The rapid pressure rise causes noisy engine running and also means that the design of the engine has to cope with a higher peak pressure. To break down the ignition delay further, it is known that in a perfectly prepared mixture suddenly raised to auto ignition conditions (temperature, pressure, etc.), there will be a delay before ignition. This is referred to as the chemical portion of the ignition delay and is the time required to form the reactive species from unreactive sources. However, the fuel and oxidizer require preparation before these chemical processes can occur. The fuel must vaporize and form a mixture within certain limits of fueltoair equivalence ratio. In a diesel engine, the fuel is injected as a liquid spray into hot gas. It then breaks up and

   forms droplets that greatly enlarge the fuels surface area, which in turn speeds the evaporation rate.

   The time taken for this preparation is referred to as the physical delay. Obviously the physical delay depends on the fuel injection system, in cylinder conditions and fuel physical properties. The chemical delay is assumed to be dependent only on fuel properties, combustion chamber conditions and equivalence ratio.

   The ignition delay of a compression ignition (CI) engine is defined as the time (or crank angle) interval between the start of injection and start of combustion [17]. This delay is due to physical and chemical processes that takes place before a significant fraction of the chemical energy of the injected liquid fuel is released. The physical processes are:

   atomization of liquid fuel jet, evaporation of fuel droplets and mixing of fuel vapour with air. The chemical processes are pre combustion reactions of fuel, air, residual gas mixture that leads to auto ignition. These processes are affected by engine design, operating variables and fuel characteristics. Ignition quality of CI engine fuels are rated by its Cetane number and the ignition delay of CI engine fuel is inversely proportional to its Cetane number. Ignition delay of CI engine plays a significant role in combustion and emission characteristics of the engine. As the delay period increases the maximum rate of pressure rise increases and also engine noise. This will lead to engine knocking which reduce the engine life. Longer delay period will retard the start of combustion closer to TDC and major portion of the fuel gets burned during expansion stroke of the piston which reduces the power developed in the engine. This also increases the BSFC and smoke emission of the engine. Shorter delay period increases the compression work against products of combustion which increase the combustion temperature and hence the NOx formation. As longer as well as shorter delay period leads to considerable side effects, the CI engine has to operate with optimum delay period for effective functioning of the engine. Ignition delay of CI engine was affected by both fuel characteristics and engine design & operating parameters. As the engine combustion and emission characteristics are influenced by ignition delay, its role is vital in diesel engine research. Research on reduction of diesel engine pollutants is progressed significantly to meet the stringent emission norms. Any methodology proposed for reducing the diesel engine pollutants has an effect on ignition delay of the engine. Research works have been carried out to reduce the diesel engine pollutants by modifying fuel injection timing. Effect of fuel injection timing on diesel engine pollutants fuelled with diesel and Bio-Diesel were investigated by many researchers.

   1. Ignition delay correlations

Arrhenus equation modied by EL-Bahnasy and El-Kotb [15] has been considered, with the help of Heywood [16] to calculate the delay period of Jatropha biodiesel blends [9] with diesel fuels as a function of cylinder pressure, cylinder temperature, and equivalence ratio as follows:

id = A P-n 1-m EXP( Ea /R – T)

One can get the coefcients A, n, m and the general empirical relation of each blend. Some equations were obtained for each blend as a function of each parameter (P, T, ).

1. Literature Review

2. Review of Various Literatures:

The literature reviews in with this topic is in below table with chronological order.

1. Conclusion:

   1. One of the above Bio-Diesel is most promising, Jatropha curcas as biodiesel renewable alternative fuel source for diesel engine is preferred to be planted over large desert areas with municipal waste water. Non-edible vegetable (green) oil derived from some plants as Jatropha that can be grown in an un- fertilized land must be widely cultivated to produce bi-diesel fuel instead of using the edible oil plants such as corn, sun-ower, and soybean.

   2. Peak pressure of B50 is higher at low and high engine speed, while that of B10 and B20 are optimum at economic engine speed (medium speed).

   3. Higher percentage of NOx in case of biodiesel compared with that of diesel is attributed to the higher combustion temperature of oxygenated biodiesel resulted from advanced injection.

   4. Mustard oil at 20% blend with diesel gave best performance in terms of low smoke intensity, emission of HC and NOx. Cetane number, total fuel consumption, specific energy consumption, specific fuel consumption, brake thermal efficiency, and cylindrical peak pressure were almost equal when engine was run on pure diesel.

   5. Experimentally investigated Single-droplet combustion characteristics have the effect at various Reynolds numbers, for Bio-Diesel and diesel.

References:

1. Dr. Tiwari, Report of Committee on Development of Biofuel Planning commission of India, April 2003.

2. S.C. Anthony Lam and Andrzej Sobiesiak, Biodiesel Droplet Combustion Journal of KONES Powertrain and Transport, Vol. 13, No. 2.

3. K. Anbumani and Ajit Pal Singh , Performance Of Mustard And Neem Oil Blends With Diesel Fuel In C.I. Engine ,ARPN Journal of Engineering and Applied Sciences ISSN 1819-6608 VOL. 5, NO. 4, APRIL 2010.

4. M. Renksizbul and M. Bussann Multicomponent droplet evaporation at intermediate Reynolds numbers, Hear Mass Transfer. Vol. 36,No. lI,pp.2827- 2835, 1993.

5. Chandrasekhar an, et al. Effect of Biodiesel, Jet Propellant (JP-8) and Ultra Low Sulphur Diesel Fuel on Auto-Ignition, Combustion, Performance and Emissions in a Single Cylinder Diesel Engine Journal of Engineering for Gas Turbines and Power, FEBRUARY 2012, Vol. 134 / 022801 by ASME.

6. Hyun Kyu Suh et.al. Spray and Combustion Characteristics of Biodiesel/Diesel Blended Fuel in a Direct Injection Common-Rail Diesel Engine

   – Journal of Engineering for Gas Turbines and Power MAY 2008, Vol. 130 / 032807 2008 by ASME.

7. C. K. LAW, Recent Advances in Droplet Vaporization and Combustion publish in Progress in Energy Combustion Science, Vol. 8. pp. 171-201.

8. Jiunn-Shyan Huang and Tsong-Sheng Lee Comparison of Single-Droplet Combustion Characteristics between Biodiesel and Diesel, ICLASS-2006 Aug.27-Sept.1, 2006, Kyoto, Japan Paper ID ICLASS06-140.

9. Mohammed EL-Kasaby, Medhat A. Nemit-allah Experimental investigations of ignition delay period and performance of a diesel engine operated with Jatropha oil biodiesel Alexandria Engineering Journal (2013) 52.page 141-149.

10. Sergei Sazhin et.al. Biodiesel Fuel Droplets Modeling of Heating and Evaporation Processes, August 2013, university of Brighton.

11. Guangwen Xu et. al. Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber published paper in Elsevier Science Ltd. PII: S0 01 6 – 2 36 1 (0 2) 00 2 76 4 page Fuel 82 (2003) 319 330.

12. C. H. Wang, X. Q. LIU, And C. K. LAW, Combustion and Micro explosion of Freely Falling Multicomponent Droplets COMBUSTION AND FLAME 56: 175-197 (1984) 175, NREL/TP-540-43672.

13. By Jinlin Xue et al. Effect of biodiesel on engine performances and emissions Renewable and Sustainable Energy Reviews journal 15(2011)1098-1116.

14. Jyotirmoy Barman et al. Experimental Investigation of Bio-Diesel Droplet Ignition, International Journal of Oil, Gas and Coal Technology, 2008 Vol.1, No.4, pp.464 477.

15. S.H.M El-Bahnasy, M.M. El-Kotb, Shock Tube Study for the Measurement of Ignition Delay Period of 1, 2-Epoxy Propane and n-Hexane. In: 6th International Conference in Fuel Atomization and Spray Systems, ICLASS-94, Ruene, France, 1994.

16. J.B. Heywood, Internal Combustion Engine Fundamentals, McGraw Hill Book Co., 1988.

17. http://personal.mecheng.adelaide.edu.au/marcus.boyd/Marcus%20Boyd%20Sho rt.pdf

18. http://www.sciencedirect.com/science/article/pii/S0016236113002172