COMBUSTION INVESTIGATIONS USING A DIESEL ENGINE CONVERTED ON OTTO CYCLE RUNNING WITH HYDROUS ETHANOL

COMBUSTION INVESTIGATIONS USING A DIESEL ENGINE CONVERTED ON OTTO CYCLE RUNNING WITH HYDROUS ETHANOL

R.L.Sari,

T.D.M. Lanzanova

J.R. Tibola

M.E.S Martins

H.A. Vielmo

Universidade Federal de Santa Maria

Departamento de Engenharia Mecânica

Grupo de Pesquisa em Motores, Combustíveis e Emissões.

Roraima Av., 1000

CP. 97105-900 Cidade Universitária, Santa Maria, Rio Grande do Sul. Brazil

Universidade Federal de Santa Maria

Departamento de Engenharia Elétrica

Grupo de Eletrônica de Potência e Controle.

Roraima Av., 7

CP. 97105-900 Cidade Universitária, Santa Maria, Rio Grande do Sul. Brazil

Universidade Federal do Rio Grande do Sul

Pós Graduação em Emgenharia Mecânica

Paulo Gama, Av, 110

CP. 90040-060 Porto Alegre, Rio Gande do Sul, Brasil

        

ABSTRACT 

This paper intends to evaluate the use of hydrous ethanol with higher water content as fuel. The engine used was an Agrale M90, air refrigerated single cylinder 0,668L, with swirl chamber indirect Diesel injection and combustion through compression ignition. Engine modifications were proposed to enable spark ignited combustion with hydrous ethanol. Fuel injection timing and spark advance management system were developed. Intake and exhaust ports instantaneous pressure and temperature, and in-cylinder instantaneous pressure were acquired. Data acquisition was performed with two National Instruments DAQs and through labview, and crank based synchronization was performed through the use of an angular encoder directly connected to the camshaft. The Three Pressure Heat Release Analysis Calculation method used to perform the combustion analysis is described and combustion related parameters are discussed for a constant BMEP and three distinct RPM.  Mixtures containing 5% and 20%  of ethanol in water were used as fuel during the tests.

Keywords: hydrous ethanol, engines, combustion analysis.

NOMENCLATURE

HCCI           Homogeneous  Charge Compression Ignition

ATDC   After Top Dead Center

RPM          Rotation per minute

TPA      Three Pressures Analysis

INTRODUCTION

Ethanol usage in Brazil dates started to grow in 1975 as a solution to overcome the world oil crisis that started in 1974 (Frank Rosillo-Calle, Luis A.B. Cortez). At that moment funds were invested in research to develop technologies to enable the ethanol use in internal combustion engines (Borges e Damasceno, 1982). Ethanol is one of the best fuels for internal combustion engines presenting elevated octane number, higher burning velocities, higher latent heat of evaporation and higher inflammability limit when compared to unleaded gasoline. (Lanzanova, T.D.M., 2013)^[a]. These properties allow operation with higher compression ratio, short combustion duration, while leaner regime (MacLean and Lave, 2003).

The main steps in the processes to obtain ethanol fuel are: crop production, transport, meshing and cooking, fermentation, distillation and dehydration. To obtain mixtures over 80% of ethanol in water the dispended energy rises exponentially. So, using ethanol with higher water content than the conventional would return direct energy savings. Figure 1 shows the energy saved when ethanol containing 35% of water in volumetric content is used in comparison with anhydrous ethanol.

Studies carried out by Cristensen and Johansson evaluated the influence of water injection in the intake manifold in a Volkswagem engine, 1.6L, naturally aspirated and in turbocharged mode. This engine presented a compression ratio of 18:1 and ran in HCCI combustion mode. To control charge auto ignition, the intake air was pre-heated. Increasing the water content allows extended operation range with no knock occurrence due to lower cylinder temperatures. Unburned HC and CO emissions presented an increase trend attributed to lower combustion efficiencies and flame quenching.  

[pic 1]

Figure 1 energetic balance comparing anhydrous ethanol and ethanol containing 35% of water (Martinez-Frias et. al., 2007)

Idaho University in partnership with RAI (Automotive Resources, Inc.) evaluated the use of catalytic igniters to burn high water content ethanol. It was chosen a mixture containing 30 % of water in ethanol to fuel the engine. Tests were carried out in a 3 cylinders engine, 0.998 liters, originally running in compression ignition mode. A new  PFI injection system was developed for wet ethanol, which enable engine operation with excess air ratio of 1.67 in SI operation mode. The combustion followed the concept of flame torch ignition. Using catalytic igniters the combustion took place in lower temperatures due to lower energy required to burn the fuel. A reduction in CO and NOx emissions was found due to the lowers temperatures attributed to the use of catalytic igniters and the increase in water percentage when comparing to the original Diesel operation.

Saxena et. al., investigated the water addition effect on the operation and combustion parameters of a 1.9 L Volkswagen engine, with 17:1 compression ratio of operating in HCCI mode. To control the ignition timing the air was pre-heated through the exhaust gases energy. With mixtures containing 20% of water in ethanol in volumetric content higher power outputs could be achieved. In a more recent work, Saxena et. al., investigated the optimum conditions for power generation using hydrous ethanol and HCCI combustion concept. All the testes were carried out in 1800 RPM using mixtures of water in ethanol from 70% to 100%. Each operation point was defined by ignition point, boost pressure and equivalence ratio. The study pointed out an optimum operation point with boost pressure of 2 bar, equivalence ratio of 0.55 and combustion timing (50% of mass fraction burned) close to 8° ATDC for mixtures containing water percentages of 30% of water in ethanol in volumetric content. As conclusion, it was found that to obtain high power output, low combustion noise, low?? NOx^[b] and in-cylinder peak pressure it is required to use high boost pressures and low equivalence ratios(high charge dilution). However, the match of these factors result in excessive unburned hydrocarbons emissions.