A Ramesh

The ignition delay of the pilot fuel in a dual fuel engine is different from that in a diesel engine because the primary fuel alters the properties of the charge, reduces the oxygen available and undergoes pre-ignition reactions during compression. In the present work, a correlation for the ignition delay in a biogas-diesel dual fuel engine has been proposed on the basis of experimental results. This correlation can be used if relevant parameters corresponding to diesel mode of operation and the properties of the gaseous fuel along with its concentration in the intake charge are known. The Hardenberg & Hase correlation for ignition delay in diesel engines has been modified for the dual fuel situation by bringing in to effect the changes in the temperature at the end of compression and oxygen concentration in the charge. The proposed correlation shows reasonable agreement with experimental results for a biogas-diesel dual fuel engine. Copyright © 1999 Society of Automotive Engineers, Inc.

Pilot fuel quantity and intake temperature are two important parameters controlling the combustion process in dual fuel engines. Experiments were conducted on a LPG diesel dual fuel engine at various intake temperatures and pilot quantities. Ignition delay, rate of pressure rise, combustion duration and heat release patterns have been presented at low and high loads. An increase in the concentration of the gaseous primary fuel significantly increased the ignition delay. At high outputs the combustion of the gas by flame propagation which follows the ignition process of the pilot and the entrained gas was the dominant feature. However, at low loads combustion of the pilot fuel and the gas entrained in it were only significant. The rapid combustion of the gaseous fuel at high output conditions, particularly when the intake temperature was high, resulted in rough engine operation. © 1998 Society of Automotive Engineers, Inc.

Conventional two-stroke spark-ignition (SI) engines have difficulty meeting the ignition requirements of lean fuel-air mixtures and high compression ratios, due to their breaker-operated, magneto-coil ignition systems. In the present work, a breakerless, high-energy electronic ignition system was developed and tested with and without a platinum-tipped-electrode spark plug. The high-energy ignition system showed an improved lean-burn capability at high compression ratios relative to the conventional ignition system. At a high compression ratio of 9:1 with lean fuel-air mixtures, the maximum percentage improvement in the brake thermal efficiency was about 16.5% at 2.7 kW and 3000 rpm. Cylinder peak pressures were higher, ignition delay was lower, and combustion duration was shorter at both normal and high compression ratios. Combustion stability as measured by the coefficient of variation in peak cylinder pressure was also considerably improved with the high-energy ignition system. © Copyright 1995 Society of Automotive Engineers, Inc.

In a dual fuel engine a primary fuel that is generally gaseous is mixed with air, compressed and ignited by a small pilot spray of diesel as in a diesel engine. Dual fuel engines suffer from the problems of poor brake thermal efficiency and high HC emissions, particularly at low outputs. In the present experimental work, the effects of intake charge temperature, pilot fuel quantity, exhaust gas recirculation and throttling of the intake on improving the performance of a LPG-diesel dual fuel engine have been studied. Results indicate that at low outputs an increase in the intake temperature and pilot quantity is advantageous. HC level generally reduces with increase in pilot quantity and intake temperature. Exhaust gas recirculation (EGR) coupled with intake heating raises the brake thermal efficiency and lowers HC emissions. With throttling and EGR there is a significant reduction in the HC levels and an improvement in brake thermal efficiency at low loads. Results indicate a possibility of determining an optimum combination of the parameters that were investigated. Copyright © 1999 Society of Automotive Engineers, Inc.