In recent years, renewable energy resources have been proposed as an alternative to petroleum-based fuels. Biodiesel, derived from vegetable oil or animal fat, is considered as an alternative renewable fuel for use in diesel engines. Biodiesels have both merits and demerits, which can be listed as follow, respectively.
The merits of biodiesel as diesel fuel, apart from their renewability, are their minimal sulfur and aromatic content, higher flash point, higher lubricity, higher cetane number and higher biodegradability and non-toxicity. Also, biodiesel contains about 10-11% oxygen by weight. Conversely, demerits include their higher viscosity, higher pour point, lower calorific value and lower volatility. Moreover, their oxidation stability is lower, they are hygroscopic and as solvents, they may be cause corrosion of components, attacking some plastic materials used for seals, hoses, paints and coating. They show increased dilution and polymerization of engine sump oil, thus requiring more frequent oil changes. Diesel engines are widely used as a power source for in-sea and on-land transportation vehicles. Though, the emissions from diesel engines are considered one of the major sources of air pollution and seriously threaten the environment and the health of living beings.
Some researchers have studied on environmental effects of the biodiesel fuels. Their studies have shown us that when biodiesel is used as a diesel engine fuel, sulfur levels, particulate matter (PM), (carbon monoxide) CO and unburned hydrocarbons in the exhaust gas are considerably less than those of conventional fuel . Researches regarding fuel economy and exhaust emissions in internal combustion engines continue to increase as a challenge. There also have been significant improvements in finding an alternative renewable fuel. Many valuable researches have been conducted on the effect of biodiesel on performance and exhaust emission characteristics of diesel engines.
Canakci investigated the effects of using biodiesel blends on the performance, combustion characteristics and exhaust emissions of a compression ignition (CI) diesel engine. In his study, the specific fuel consumption (SFC) increased with the addition of biodiesel to conventional diesel fuel.
Ozener with some researchers carried out a study on combustion, performance and emission characteristics of a diesel engine operating with petroleum-based diesel and biodiesel blends obtained from soybean oil. It was shown that SFC could be decreased by using biodiesel blends in diesel engines.
In Xue’s investigation, biodiesels from waste edible oil have been reviewed to summarize the effects of biodiesel combustion on the combustion characteristics, engine performance and emissions.
In a study conducted by Can , biodiesel fuels produced from two different kinds of waste cooking oils were blended with No. 2 diesel fuel and their effects on the engine performance and emissions were examined. As a result of his study, the ignition delay with the biodiesel addition was decreased for all loads with the earlier combustion timings. For the time being, the maximum heat release rate and the in-cylinder pressure rise rate were slightly diminished and the combustion duration was generally increased with added biodiesel. While there were no significant changes on CO emissions at the low-medium engine loads, some reductions were detected at the full load. CO2 emissions were slightly increased for all loads.
Ramadhas with some researchers investigated the effects of engine load and biodiesel percentage on the SFC of a four-stroke DI, naturally aspirated single-cylinder diesel engine. According to their experimental evaluations, the lower biodiesel blends increased the brake thermal efficiency and diminished the fuel consumption and exhaust emissions were decreased with rise in biodiesel concentration. Consequently, their experimental results proved that usage of biodiesel, which was produced from unrefined rubber seed oil, in CI engines was an alternative to diesel.
Tesfa with some researchers performed experimental studies to investigate the influence of biodiesel properties on the combustion and performance characteristics of a CI engine. They seen that the biodiesel types did not lead to any differences in specific fuel consumption and peak cylinder pressure. The specific fuel consumption for the engine running with neat biodiesel (No diesel fuel addition) was higher than the engine running with normal diesel by up to 15%.
Muralidharan with some researchers examined the combustion, emission and performance characteristics of a single cylinder; four stroke, variable compression ratio, diesel engine fueled with waste cooking oil methyl ester and its blends with conventional diesel. It was seen that the performance of the B40 blend is worthy when compared with the conventional diesel at full (%100) load. Also, there was small rise in NOX emission. Though, They draw a conclusion that it was still comparable with that of standard diesel fuel and was in the suitable range, as well.
Gonca investigated the effects of steam injection on the performance and NO emission of a diesel engine fueled with ethanol , hydrogen and examined the effects of steam injection on equilibrium combustion products and thermodynamic properties of bio fuels. In the results, it was reported that the steam injection method decreases the NO formation of the diesel engine fueled with bio fuels and hydrogen. Many experiments based on combustion simulations and thermodynamics have been carried out to optimize the performance of the diesel engines and its cycles which are classical diesel cycle, dual cycle and Miller cycle.
Chen with some researchers conducted a thermo dynamical performance analysis of an air-standard dual cycle by taking into account the heat-transfer and friction-like loss terms. The results showed that the friction and heat transfer losses considerably abate the engine performance.
Ozsoysal determined the combustion efficiency of a dual cycle as a percentage of the fuel’s chemical energy. As a result, the combustion efficiency decreased with increasing losses.
Ebrahimi studied on the performance analysis of an air standard dual cycle based on the FTT. It was shown that equivalence ratio and mean piston speed remarkably affect the engine performance and there are optimum points for the equivalence ratio and mean piston speed.
Ust with some researchers examined the impacts of the heat transfer losses and combustion on the work output, mean effective pressure and thermal efficiency of an air-standard irreversible dual cycle by using combustion and heat transfer constants. The results demonstrated that engine performance increase with decreasing heat transfer constant and raising combustion constant.
Parlak conducted an optimization study for the irreversible dual and diesel cycles based on the maximum power and maximum thermal efficiency criteria. In the results, it was claimed that the performance of the dual cycle is higher in comparison with the diesel cycle.
Al-Hinti with some researchers evaluated the net power output and cycle thermal efficiency of air-standard diesel cycle by using realistic parameters such as airefuel ratio, fuel mass flow rate, intake temperature. They asserted that the cycle performance decreases with increasing intake temperature, air-fuel ratio and fuel mass flow rate.
Gonca with some researchers applied the Miller cycle into a diesel engine computationally and experimentally to abate NO emissions and increase the effective efficiency. They achieved noticeable NO reduction with the application of the Miller cycle.
Gonca and Sahin investigated the effects of engine design and operating parameters on the performance of a turbocharged and Miller cycle diesel engine with steam injection method.
Gonca conducted a thermodynamics analysis and presented performance maps for a DualAtkinson cycle engine based on finite-time thermodynamics and classical thermodynamics .
Wang with some researchers achieved the reduction of NOx emissions by experimentally applying the Miller cycle into a diesel engine.
Sarkhi with some researchers investigated the impacts of the variable specific heats of the working fluid on the performance for an air standard reversible Miller cycle and irreversible Miller cycle . In another study, Sarkhi with some researchers analyzed the cycle performance by using the maximum power density criteria. In their studies, the Miller cycle provide higher cycle performance compared to other gas cycles.
Zhao and Chen conducted a performance analysis for anair standard irreversible miller cycle with respect to the change of the pressure ratios. The results showed that pressure ratios remarkably affected the cycle performance.
Ebrahimi analyzed an air standard reversible Miller cycle with respect to variation of engine speed and variable specific heat ratio of working fluid and he analyzed an air standard irreversible Miller cycle with respect to the variation of relative airefuel ratio and stroke length. They proved that engine performance changes with the engine speed, variable specific heats, relative airefuel ratio and stroke length.