Concept of Reactivity Controlled Compression Ignition on a Single Cylinder Automotive Engine

Abstract

The cost of conventional fuels is increasing day by day. To overcome this, alternative fuels are getting more and more attention with additional benefits of exhaust emission reduction and in delaying faster depletion of crude oil reserves. Because of better fuel economy of Compression Ignition (CI) engines, users have been preferring these not only for off road vehicles but recently even for on highway passenger vehicles. An important feature of CI engine is that it can tolerate wide variety of fuels and this includes both liquid and gaseous fuels. Continuous research is going on in technologies like hybrid, biofuel vehicle, etc. to make them able to produce greater power than conventional diesel engine. Also, now a days for transportation, users are relying more on natural gas due to its lower price and not only it has cut running cost but has also made people less dependable on premium liquid petroleum products like Ultra low Sulphur Diesel. To retain fuel economy benefits of CI engine and tailpipe emission of gaseous fuel spark ignition engine, one of the available options is the dual fuel technology, also now a days known as Reactivity Controlled Compression Ignition (RCCI) technique. This technique has an advantage that the dual fuel engines need very less modifications to convert it from diesel engine and by this technology one can vary the reactivity inside the combustion chamber by varying the quantity of fuels of entirely different reactivity. Here high reactive fuel is used only for making the flame propagate throughout the low reactive air fuel mixture in combustion chamber at constant rate. In most of the cases, Compressed Natural Gas (CNG) is used as a low reactive fuel and diesel or B20 fuel as a high reactive fuel. Fuels like ethanol and petrol can also be used as a low reactive fuel but CNG being in gaseous form requires less modification to use it as a low reactive fuel. CNG can be mixed with air through port injection or direct injection. Subsequently, the amount of diesel injected inside cylinder is decreased in proportion of injected gaseous fuel. Amount of CNG that can be mixed is entirely limited by exhaust emissions of HC, CO and knocking produced inside the cylinder. According to the literature survey done, the maximum diesel substitution is 70%. For this project 650 cc diesel, water cooled engine is taken as baseline engine with rated power of 10.8 kW @ 3200 rpm and maximum torque of 38 Nm @1600 rpm with compression ratio of 19.2:1 having re-entrant type piston bowl. By analysing the design and packaging of current engine, it is required to modify intake manifold for CNG port injector and Temperature Manifold Absolute Pressure (TMAP) sensor mounting, and finally modify the piston bowl volume and shape for lower compression ratio in the range of 15 to 17:1 for better air utilisation. 7 GT-Power software of Gamma Technology is used for one dimensional simulation of baseline and modified engine performance. This simulation predicts the peak cylinder pressure achieved during combustion, performance and emission. Initially separate models of baseline engine with Diesel and CNG as single fuel are made in the software. Then this model is converted to RCCI to study the effect on performance and emission by varying percentage of fuels. Then the results are verified with help of engine steady state performance test