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Experiments were conducted on a single cylinder SI engine fuelled by natural gas. Equivalence ratios varying from 0.7 to 1.0 were used and the spark timing was changed from no knock to high knock conditions. Pressure crank angle data from 160 consecutive cycles was analysed. It was found that coefficient of variation of peak pressure (COVPP) and standard deviation of the angle of occurrence of peak pressure (SDAPP) can be used to set the engine for knock free operation. These parameters show a sudden rise from a minimum value that they attain near a spark timing where knock sets in. When the average knock intensity is low, there are two groups of cycles. The first comprises of non-knocking to slightly knocking ones. The other contains cycles with relatively high knock intensity. The sudden emergence of two groups is responsible for the observed trends of SDAPP. At high overall knock intensities the first group is absent.

Experiments were conducted on a single cylinder, natural gas fuelled spark ignition engine. Air fuel ratio was varied from about stoichiometric to the lean limit at two different throttle positions with optimum spark timing. Subsequently the engine was tested at constant throttle and equivalence ratio with variable spark timing. COV (coefficient of variation) of IMEP (indicated mean effective pressure) and peak pressure increase with a reduction in equivalence ratio. When the engine starts to misfire there is a drastic increase in the COV of IMEP. Spark timing has a smaller effect on COV of IMEP than on COV of peak pressure. When the spark timing is advanced, COV of peak pressure attains a minimum value just before knock sets in. Prior cycle effects were seen when there was misfire. Spark timing had little influence on the frequency distribution of IMEPs of cycles, which was generally symmetrical about the mean.

A diesel engine was operated with karanja oil, bio-diesel obtained from karanja oil (BDK) and diesel as pilot fuels while LPG was used as primary fuel. LPG supply was varied from zero to the maximum value that the engine could tolerate. The engine output was kept at different constant levels of 25%, 50%, 75% and 100% of full load. The thermal efficiency improved at high loads. Smoke level was reduced drastically at all loads. CO and HC levels were reduced at full load. There was a slight increase in the NO level. Combustion parameters indicated an increase in the ignition delay. Peak pressure and rate of pressure rise were not unfavorably affected. There was an increase in the peak heat release rate with LPG induction. The amount of LPG that could be tolerated with out knock at full load was 49%, 53% and 61% on energy basis with karanja oil, BDK and diesel as pilots.

In a dual fuel engine a primary fuel that is generally a gas is mixed with air, compressed and ignited by a small pilot- spray of diesel as in a diesel engine. Dual fuel engines generally suffer from the problem of lower brake power and lower peak engine cylinder pressure due to lower volumetric efficiency, although an improvement in brake specific energy consumption is observed compared to pure diesel mode. Results indicate that with an increase in percentage of CNG substitution the brake power decreases. The exhaust gas temperature and peak cylinder pressure also decrease. The rate of pressure rise is higher at lower engine speeds (1100, 1400 rev/min), although at 1700 and 2000 rev/min it is lower. The delay period throughout the engine speed shows an increasing trend. The coefficient of variation is also higher throughout the engine speeds and shows an increasing trend. The brake specific energy consumption is lower at 1100, 1400 and 1700 rev/min and at 2000 rev/min it is higher.

The increasing use of natural gas as a vehicle fuel has generated considerable research activity to characterize the performance of engines utilizing this fuel. A light duty prechamber diesel engine was run under naturally aspirated and turbocharged CNG- Diesel dual fuel mode at four engine speeds 1100, 1400, 1700 and 2000 rpm. The maximum percentage of CNG substitution continues up to the engine knock limited power. The experimental results indicate a fall in brake power under naturally aspirated CNG-Diesel dual fuel mode compared to neat diesel operation. It was due to decrease in volumetric efficiency and slower combustion. Although turbocharged dual fuel operation shows an increase in brake power as well as an improvement in brake specific energy consumption as it provides a better air/fuel mixing and improves the homogeneous natural gas/air charge.

Experiments were conducted to assess the relative effects of swirl (by using a masked intake valve and by providing swirl grooves on the piston crown) and squish on the performance, emission and combustion characteristics of a lean burn engine operating on liquefied petroleum gas (LPG) at a compression ratio of 10.5 under 20% and 100% throttle opening conditions. The swirl produced by the masked intake valve configuration at 100% throttle opening resulted in improved thermal efficiency and reduced HC emission, cyclic variations, ignition delay & combustion duration as compared to swirl groove piston and enhanced squish piston. The lean misfire limit was extended and there was no increase in the NO level at any given power output. At 20% throttle with high squish, under lean mixture conditions, combustion is even better than the masked valve configuration.