Elsevier

Energy

Volume 36, Issue 6, June 2011, Pages 3917-3923
Energy

Durability studies of mono-cylinder compression ignition engines operating with diesel, soy and castor oil methyl esters

https://doi.org/10.1016/j.energy.2010.10.037Get rights and content

Abstract

There are many studies showing that the performance results for engines operating with biofuels are acceptable, although very few long-term analysis of wear and maintenance problems are shown. Three mono-cylinder compression ignition engines were tested for approximately 1000 h each, with pure diesel oil (D100), pure soy methyl ester (SME100) and pure castor oil methyl ester (CME100). The lubricating oil analysis didn’t reveal any excessive amount of metals compared to the engine with pure diesel. Viscosity decreased very soon to values below the minimum recommended due to dilution with the methyl esters, especially with SME100. The injection system analysis showed that opening pressures, hydraulic flux and corrosion levels were acceptable. The SME piston showed a very small crack. A higher amount of carbon deposits and gum formation was found over biofuel pistons, indicating poor combustion. Piston ring seating and gap were inside specification. Cylinder liners presented no damage on running surface. The valves presented abrasive and adhesive wear, contact fatigue for SME100 and marks at valve seating for CME100, considered acceptable after 1000 h of test. The results obtained show that the use of pure methyl esters fuels was acceptable for these engines regarding wear and maintenance problems.

Introduction

A review [1] made with many studies using vegetable oils (soy, rapeseed, canola, sunflower, cottonseed and similar oils), but not transesterified, as a replacement for diesel fuel, particularly during the early 1980s, showed favorable results for short-term engine tests for the majority of these studies; however, for long-term durability tests, severe problems with carbon deposits and lubricating oil contamination were identified. Several investigations carried out on the 90 decade and early 2000s on the use of straight and transesterified vegetable oils in internal combustion engines are described in [2]. In this article, the authors summarize the experimental results of short-term engine tests based on performance and emissions, and they also provide a description of a few studies on extended operation, whose results are very similar to those indicated in Jones and Peterson, i.e., the main problems observed in the engines refer to the buildup of carbon deposit and sticking of piston rings.

The emissions characteristics of a diesel engine were studied in [3] when operating on rapeseed methyl ester, which showed that both carbon monoxide and unburnt hydrocarbon decreased compared to pure diesel. CO2 concentrations and fuel consumption were a little higher and exhaust temperatures were very similar. After 33 h of operation the lubricating oil viscosity decreased because of fuel dilution and the author states that the engine conditions showed satisfactory overall appearance, indicating reasonable behavior of lubricating oil under sustained dilution. Also Karaosmanoglu et al. [4] studied engine behavior with sunflower oil for a 50-h-period (considered long term) and didn’t observe any remarkable changes. The results were considered promising for this fuel although diesel engines are expected to last much longer than 50 h. Another study [5] considered 100 h as long term but the objective was the characterization of the deposits to suggest additives to the fuel. The results showed a higher amount of fixed carbon in the deposits for emulsified palm oil, but at the same time NOx emissions decreased. Many authors have studied engine performance with vegetable oil methyl esters [6], [7], [8], [9], [10], [11], [12] and the results usually show a slight decrease in torque and power along with an increase in specific fuel consumption. Emission results may differ from one author to another but they usually report fewer emissions of CO, HC and smoke while NOx increases with biofuels.

Some authors suggest the importance of studying the engine wear resulting from the use of vegetable oils and its transesterified form. In [13], [14] the results of metal content tests on lubricant oils are shown to assess the engine wear of 12 Dodge pickups equipped with the 5.9 l Cummins diesel engines fueled with zero, one, two, 20, 50 and 100% blends of diesel oil and biodiesel of soybean, canola, and rapeseed. An analysis of engine lubricating oil taken when the oil was changed in the vehicles (every 4800 km for B100 pickups) was compared to the analysis of oil samples pulled from 100% petroleum fueled diesel engines during approximately 150,000 km. The findings suggested that the biodiesel and biodiesel blend fueled engines were wearing at a normal rate. In fact, the replacement of diesel with biodiesel reduced the wear of aluminum, iron, chromium and lead components in the diesel engines tested. Interesting results were found in [15] regarding some tribology characteristics of a bus diesel engine after 110 h running with rapeseed biodiesel. The items investigated were the pump plunger surface roughness, carbon deposits in the combustion chamber, injector, and injector nozzle holes. Root mean square roughness determined through an electronic microscope decreased from 0.45a to 0.4a after biodiesel usage what indicates improved lubricant conditions. Deposits at injectors and combustion chamber were determined using endoscopic inspection and the visual aspect showed that injectors became cleaner after biodiesel usage, and the amount of deposits was the same, although with a different distribution. The injector nozzle holes were studied through its discharge coefficient and the biodiesel influence was rather smaller with only one noticeable variation. A different approach was used by Tarkowski et al. [16] who studied the deposits of two bus engines fueled with standard diesel (SO) and ecological City-diesel (C-D) after 70,000 km. Light elements were determined by a CHN analyzer while for other elements X-Ray florescence was used and also Mössbauer measurements for the magnetic components. The improved fuel (C-D) presented decreased content of both light (carbon, hydrogen and nitrogen) and heavy elements (particularly iron); therefore, smaller attrition of steel elements might be expected.

Typical levels of metal on lubricant oil of diesel engines are suggested in Haycock and Hillier [17] and their interpretation is provided for guidance. In Table 1, these levels and interpretations are presented.

The determination of the metal content on lubricant oils is a means of identifying engine defects due to the wear process at an early stage which permits remedial action before any really serious damage may occur. Today, the techniques used to determine the metal content are the spectrographic oil analysis and the ferrographic oil analysis. According to Morley [18], the spectrographic technique depends on the observation that when the atoms of an element are excited, for example, by means of a flame, or an electrical discharge, they emit electromagnetic radiations which are uniquely characteristic of that particular element. The method determines metal concentrations on used oil in parts per million [ppm] and it disregards particles whose size exceeds 2 μm as a result of its failure to atomize such particles. Ferrography is a monitoring method of examination based on the extraction of ferromagnetic and paramagnetic particles from lubricant sample by means of a magnetic field, and quantifies the metal particles in the form of DL and DS values for large (greater than 5 μm) and small particles, respectively [19], [20].

Section snippets

Materials and test procedures

To perform the durability tests, three single cylinder Agrale M93ID direct injection engines with cylinder assembled at vertical position were used, whose specifications are the following:

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    90 mm piston nominal bore;

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    105 mm piston stroke;

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    20:1 compression ratio;

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    668 cm3 piston displacement;

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    17° BTDC end of injection angle;

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    10.8 kW (14.7cv) at 2750 rpm (ISO 3046 Standard) of maximum power (F curve);

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    180 + 8 bar injector opening pressure;

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    injector type S with 4 × 0.8 mm machined holes.

Each engine was coupled to an

Results and discussion

The evaluation results of the engines were divided into two groups for analysis: lubricating oil and internal parts.

Conclusions

A long-term analysis of 1000 h was conducted to evaluate the durability of three mono-cylinder diesel engines fueled with castor oil methyl ester (CME100), soy methyl ester (SME100) and diesel (D100) according to a time and load cycle. Lubricating oil samples were collected every 50 h. Main components were measured and evaluated by their OEMs after the end of the test.

The lubricating oil analysis revealed a great viscosity decrease due to dilution with SME100. The oil spectroscopy showed low

Acknowledgements

The authors would like to thank the Departments of Mechanical Engineering and Chemistry of the University of Caxias do Sul, Agrale S.A. Company, and the Brazilian Ministry of Science and Technology (MCT) for the funding support.

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    Citation Excerpt :

    And this concentration of wear metals from engine components possessing some warning limits and if these wear metals exceeding the prescribed warning limits indicates the severe wear in the engine cylinder. The main elements from the engine cylinder wear include iron, aluminium, copper, lead, tin, chromium, silicon and boron and each of these metals having its own warning limit which was mentioned in the Table 6 [55]. The wear of different crucial parts of the engine may be reduced to significant level due to the added lubricity properties of biodiesel, deposits of carbon on the piston top and injector coking significantly declined and also it was observed that the content of ash representing the metal wear debris was reported lesser biodiesel fueled engine [55].

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