Investigations of a Direct Injection Diesel Engine Run on Non Petroleum Fuel Blends

Abstract

The accumulation of waste automobile tyres causes a severe environmental problem, and also contaminates the soil and reduces the fertility. The anthropogenic gases raise from the disposal area is one of the reasons for the increase in greenhouse gases (GHGs). The burning of automobile tyres is toxic and harmful to the human being. Therefore, it is very much essential to dispose the waste tyres in an efficient way.
Pyrolysis process is one of the methods to recycle the waste automobile tyres in to useful energy. In the pyrolysis process, long chain polymers are thermally broken down into smaller hydrocarbon in the oxygen free environment. The process yields three principal products, viz., tyre pyrolysis oil (TPO), pyro gas and carbon black. The TPO consists of C, H, O, N and S containing organic compounds and water. The organic compounds range from C5 to C20. The TPO contains fractions of volatility consistent with gasoline, kerosene and diesel. As a result, the TPO was examined as an alternative fuel in both spark ignition (SI) engines and compression ignition (CI) engines. The solid carbon black can be used in industrial application such as re-treading, coating of insulation and industrial filters.
The main drawback of TPO is its lower cetane number due to which it can not be used as sole fuel in diesel engine. The cetane number of TPO is in the range of 25-30. This issue can be resolved by blending TPO with a fuel of higher cetane number. In this regard, the TPO was blended with Jatropha methyl ester (JME), whose cetane number is higher than that of diesel, and used as an alternative fuel in a single cylinder, four stroke, air cooled, direct injection (DI) diesel engine developing 4.4 kW. In this research study, seven modules of work were carried out that include six experimental and one optimization. Experiments have been conducted by using five different blends where TPO was blended, from 10 to 50% at steps of 10% on a volume basis with JME. The blends were denoted as JMETPO10, JMETPO20, JMETPO30, JMETPO40 and JMETPO50, where the numeric value represents the percentage value of the TPO in the Jatropha methyl ester tyre pyrolysis oil (JMETPO) blend. The combustion, performance and emission behaviour of the engine fueled with the JMETPO blends, were compared with those of diesel and JME operations. The test results indicated that, the JMETPO20 blend exhibited reasonably better performance and lower emissions than those by other JMETPO blends. The brake thermal efficiency for the JMETPO20 blend was close to that of diesel at full load. Further, the brake specific carbon monoxide (BSCO), brake specifc hydrocarbon (BSHC) emission and smoke opacity also reduced by 9.1%, 8.6% and 26% respectively, compared to those in case of diesel at full load. Interestingly, the combustion, performance and emission behaviour of the engine deviated after 20% TPO in the blend.
In the second module of the research work, a new approach was employed to develop hybrid multi criteria decision making techniques namely VlseKriterijumska Optimizacija I Kompromisno Resenje (in Serbian) (VIKOR) for ranking the blend alternatives. The proposed model, principal component analysis was integrated with a technique VIKOR to determine an optimum JMETPO blend. The experimental results of the combustion, performance and emission parameters of the test engine operated with different JMETPO blends at different load conditions were used for optimization. It was noticed that experimental trial number 32 had the smallest VIKOR index (Qi) value for JMETPO20 blend compared to other JMETPO blends. Thus, it was concluded that, the minimum VIKOR index can be obtained when engine was operated with the JMETPO20 blend at full load. Thus, the final ranking for the JMETPO blends based on VIKOR analysis was JMETPO20> JMETPO10> JMETPO30> JMETPO40> JMETPO50.
In the third module, the effect of varying the injection timing on the combustion, performance and emission characteristics of the test engine was experimentally investigated, when the engine was run with the JMETPO20 blend. The original injection timing was altered by adjusting the number of shims fitted under the plunger in the pump, by addition or removal of shims. In addition to the original injection timing of 23 ˚CA bTDC, other injection timings at which the study was carriedout were 20, 21.5, 24.5 and 26 ˚CA bTDC. The results indicated that, the blend gave a better performance and lower emissions when operated with an advanced injection timing of 24.5 ˚CA bTDC as compared to other injection timings.
In the fourth module, the tests were conducted at the optimum injection timing to study the effect of the nozzle opening pressure on the combustion, performance and emission characteristics of the test engine fueled with JMETPO20 blend. In order to find an optimum nozzle opening pressure for the blend, tests were conducted at an optimized injection timing with five nozzle opening pressure s viz. 210, 220, 230, 240 and 250 bar in addition to the original nozzle opening pressure of 200 bar, and the findings were compared with those of diesel operation. Based on the combustion, performance and emission of the engine, the nozzle opening pressure of 220 bar gave a better performance results and lower smoke, and BSHC and BSCO emissions compared to other nozzle opening pressure investigated.
Further, study was carriedout at investigating the effect of varying the compression ratio at optimized injection timing and nozzle opening pressure on the behaviour of the test engine, using optimum blend, i.e. JMETPO20. The engine was subjected to one lower (16.5) and one higher (18.5) compression ratio in addition to the standard compression ratio of 17.5. At the higher compression ratio of 18.5 and full load, shorter ignition delay, maximum cylinder pressure and higher heat release rate were found for the blend, compared to those in case of the original compression ratio. The increase in the compression ratio from 17.5 to 18.5 for the blend improved the brake thermal efficiency by about 8% compared to that of the original compression ratio at full load. The BSCO, BSHC emissions and smoke opacity were reduced by about 10.5%, 32%, and 17.4% respectively, with respect to those of the original compression ratio at full load.
The oxidation stability of biodiesel plays an important role for its long term storage. Although it is possible to obtain the required oxidation stability of any biodiesel by using synthetic antioxidants, at the same time, it will increase the cost of the resultant fuel as antioxidants are expensive. The phenolic compounds present in the pyrolysis oil may act as natural antioxidants to biodiesel. TPO derived from waste automobile tyres through pyrolysis contains few phenolic compounds. Therefore, in the sixth module of this research work, an attempt was made to analyse the influence of blending different amounts of TPO with JME on the oxidation stability of the blend. For this purpose, 20%, 40% and 60% (on volume basis) of TPO were blended with the JME. This work reveals that, blending TPO with JME, there was a significant improvement in the oxidation stability of JMETPO blends. In addition to this, an experimental investigation was also carriedout by using the JMETPO20 blend, to evaluate the behaviour of the diesel engine run on the biodiesel blend, with and without syntheticantioxidants. Based on the experimental findings, this study suggests that blending 20% TPO with 80% JME can reduce dosage of antioxidant by about 50%.
Finally a comparative study was conducted in this module to examine the durability issues of a direct injection diesel engine run on the JMETPO20 blend and diesel. For this purpose, the engine operated with the JMETPO20 blend and diesel was run for 100 h, which consist of 14 test cycles of 7 h each as per the IS 10000 standards. Visual examination of the vital parts of the engine components such as cylinder head, piston crown, and nozzle injector tip etc. was also carried out to find the carbon deposit after the durability test. After the durability test, several tribological characteristics of the used lubricating oil were evaluated after every 25 h of engine operation in order to analyze the consequence of fuel chemistry on the life of the lubricating oil. Measurement of different metal debris concentrations present in the lubricating oil samples drawn from the JMETPO20 blend and diesel operated engine was carriedout by the atomic absorption spectroscopy. On the whole, it is concluded that, the JMETPO20 blend can be used as an alternative fuel for CI engine with few minor modifications in the engine geometry.