Demand for the petroleum products is increasing continuously at a global level and their existence comes to an end soon in future. Also, they produce large amounts of exhaust emissions when used in internal combustion (IC) engines. Diesel engines, in particular, emit a higher quantity of toxic engine exhaust emissions, which are harmful to living things especially human beings. This demands feasible, sustainable and renewable energy resources to solve the above two concerns mentioned. The advancement in IC engine technology powered with the combination of biofuels both liquid and gaseous fuels also contributed a lot in addressing the above two issues. The work reported here focuses on the development of new combustion concept called homogeneous charge compression ignition (HCCI) engine with a high-pressure injection system to inject biodiesel in combination with gaseous fuel to address the above two issues. The extensive use of a combination of both biodiesel and gaseous fuel will pave way for the energy security of the country besides not affecting to global climate change.

The extensive work reported here is broadly classified into Production of Biodiesel, dual fuel (DF), Common rail direct injection (CRDI) and homogeneous charge compression ignition (HCCI) engines operations:

1. Biodiesel Production
   Transesterification is a process in which chemical reactions taking place between triglycerides of vegetable oil and methyl alcohol to produce biodiesel. A catalyst (NaOH/KOH) was used to enhance the reaction. Fatty acid ester and glycerol are the byproducts of the reaction. Biodiesel production plant of 50 litres capacity is shown in Figure 1. The main purpose of the transesterification process is to reduce free fatty acid (FFA) and viscosity significantly. Boiling point and flash point were also reduced with lower glycerides and enhanced Cetane number (CN). In the process, 1% NaOH catalyst or KOH (% mass basis) is added to 20% methanol (by volume) and mixed with 1 litre of selected vegetable oil. This mixture is heated to a temperature of 70oC and stirred at a speed of 200 – 250 rpm. Triglyceride content of the vegetable oil reacts chemically with three molecules of alcohol. A catalyst used enhances the reaction. Finally, a mixture of fatty acids along with the content of glycerol was obtained. Better conversion from mother oil to biodiesel was possible with 3:1 molar ratio of alcohol to triglycerides. Generally a higher ratio of alcohol to oil ratio use is a practice to obtain biodiesel of lower viscosity and higher yield. Set up to remove the dissolved catalyst from Biodiesel is shown in Figure 2. This process is best suited when the selected oil has an acid-value less than 1%. This method yields more than 98 % conversion efficiency with minimal side reactions.
   

   Figure 1: Biodiesel Production Plant

   

   Figure 2: Set up to remove the dissolved catalyst from Biodiesel

    

2. Dual Fuel Engines
   Rapid depletion of crude petroleum fuel with increased prices and also with the aim to meet the environmental legislation, it is mandatory to use environment-friendly alternative fuels in the current engines to partial or complete replace the diesel fuel. The additional cost of the compressed natural gas (CNG) / liquefied petroleum gas (LPG) / Hydrogen equipment is compensated by the cheaper price of the gas fuel over the vehicle’s lifetime. DF engines have drawn substantial research because conventional engine operates without any major modifications and have the flexibility of switching back to the diesel mode. Biodiesel and gas fuel combination in DF mode is an attractive way for countries with agriculture base. Figure 3 depicts the DF engine set up.
   

   Figure 3: Dual Fuel Engine setup

   Links: 
   - http://doi.org/10.1016/j.renene.2018.01.049; http://doi.org/10.1016/j.renene.2016.03.010    - http://dx.doi.org/10.1016/j.renene.2016.08.002; http://dx.doi.org/10.1016/j.fuel.2017.01.08

3. Common Rail Direct Injection (CRDI) Engines
   The experimental investigations on a diesel engine fitted with CRDI facility is an effort towards the reduction of exhaust emissions without compromising the fuel efficiency. This work demonstrates the performance, combustion and engine emissions of a single cylinder, four-stroke, water cooled, CRDI engine powered with biodiesel by varying the operating parameters like fuel injection timing, fuel injection pressure, injectors with different holes and exhaust gas recirculation. Figures 4 and 5 respectively show the CRDI engine set up developed in-house and CDRI injectors*. An electronic control unit (ECU) developed in-house for fuel injection and diesel fuel spray from CRDI injector are shown in Figures 6 and 7. Exhaust gas analyzer and smoke meter are given in Figures 8 and 9 respectively.

    

    

   
   Links: 
   https://doi.org/10.1016/j.energy.2017.08.035; http://dx.doi.org/10.1016/j.rser.2016.11.058

4. Homogeneous Charge Compression Ignition (HCCI) EnginesThe rapid depletion of petroleum fuel associated with its higher price and environmental legislation mandates use of environment-friendly alternative fuels that replace diesel either partially or completely. In HCCI engine operation, a homogeneous air-fuel mixture prepared for auto-ignition by compression alone at a number of locations within the combustion chamber on reaching the chemical activation energy. The chemical kinetics controls the control combustion process. This technology provides higher brake thermal efficiency (BTE), ability to use a variety of alternative fuels that includes diesel, hydrogen, natural gas, propane, butane, ethanol and dimethyl ether besides lower oxides of nitrogen and particulate matter (PM) emissions. Knocking due to premature combustion before the piston reaches the top dead centre (TDC), high levels of hydrocarbon (HC) and carbon monoxide (CO) are inevitable with HCCI engines. Figure 10 depicts the HCCI engine setup*.
   

   Figure 10: HCCI Engine setup

   Link: https://doi.org/10.1016/j.renene.2018.08.035