A Ramesh

In a biogas diesel predominantly premixed charge compression ignition (BDPPCCI) engine the effect of composition of biogas on combustion, performance and emissions was experimentally investigated. A twin cylinder automotive common rail engine with an open electronic control unit was run on one of its cylinders in this mode while the other cylinder was nonfunctional. Three biogas compositions with methane (CH4) proportions of 53–58% (as obtained from the plant), 67% and 22–25% were used at a constant engine speed of 1800 rpm. Stable engine operation in the BDPPCCI mode even with very low methane fractions was possible without adverse effects on efficiency and emissions. Reducing the methane proportion (i.e. high proportion of CO2) enabled the brake mean effective pressure (BMEP) to be extended from 4 bar to 5 bar with sufficient margin for start of injection (SOI). Lower CH4 (i.e. increased CO2 proportion) also allowed the use of retarded SOI for diesel which resulted in reduced smoke emissions. This not only improved the combustion phasing but also lowered the peak heat release rate leaving the thermal efficiency relatively unaffected. Results indicate that extremely low levels of NO and smoke can be reached in the BDPPCCI mode at the best efficiency operating condition if the biogas composition is altered based on the output.

In dual fuel engines auto-ignition of the inducted butanol creates a high temperature environment prior to the injection of diesel. This results in enhanced smoke emissions. This work was aimed at controlling the smoke level in a butanol diesel common rail turbocharged dual fuel engine through multiple fuel injections. Experiments were performed on a three cylinder turbocharged common rail diesel engine at a speed of 1800 rpm and BMEPs corresponding to 75% and 100% of full load (BMEP of 11.8 bar). Port fuel injectors along with dedicated circuitry were employed to control the quantity and timing of butanol introduction into the intake air. An open engine controller was used to vary the rail pressure, injection timing and number of pulses of the diesel that was directly injected into the combustion chamber. The injection timing of diesel was always set for best efficiency. First the effect of Main plus Post Injection (MPI) of diesel at a fixed butanol to diesel energy share (BDES) of 30% was evaluated at different post injection quantities and main to post offsets. Subsequently the influence of BDES was studied at a fixed post injection quantity and offset from the main injection. Finally Pilot plus Main Injection (PMI) of diesel, Main plus Post Injection (MPI) of diesel and Main plus Two Post Injections (MPTPI) of diesel were compared in the dual fuel mode. MPI resulted in improved brake thermal efficiency (BTE) and drastically reduced the smoke level because of enhanced mixing by the momentum of the post injected fuel. NO and CO2 were also reduced. Using high BDES values along with optimised post injection quantities and main to post offsets reduced the smoke level. PMI of diesel resulted in lower BTE and higher smoke, while the only advantage was reduced NO levels. MPI was better than MPTPI with respect to all the parameters. On the whole, in a dual fuel engine that uses butanol and diesel the main plus post strategy is effective in improving energy efficiency, reducing smoke and also in increasing the amount of butanol that can be utilized.

Abstract Improvements in a two-stroke, spark-ignition (2S-SI) engine can be realized by curtailing short-circuiting losses effectively through direct injection of the fuel. Liquefied petroleum gas (LPG) is an alternative transportation fuel that is used in several countries. However, limited information is available on LPG fuelled direct injected engines. Hence, there is a need to study these systems as applied to 2S-SI engines in order to bring out their potential benefits. A manifold injected 2S-SI engine is modified for direct injection of LPG, in gaseous form, from the cylinder head. This engine is evaluated for performance, emission and combustion. Evaluation at various throttle positions and constant speed showed that this system can significantly improve the thermal efficiency and lower the hydrocarbon (HC) emissions. Up to 93% reduction in HC emissions and improved combustion rates are observed compared to the conventional manifold injection system with LPG. CO emissions are higher and peak NO emissions are lower with this system due to the presence of richer in-cylinder trapped mixtures and charge stratification. This system can operate with similar injection timings at different throttle positions which make electronic control simpler. It can work with low injection pressures in the range of 4-5 bars. All these advantages are attractive for commercial viability of this engine.