The effects of biomass syngas composition, moisture, tar loading and operating conditions on the combustion of a tar-tolerant HCCI (Homogeneous Charge Compression Ignition) engine

• A novel tar tolerant HCCI engine system for biomass gasification is introduced.
• Artificial syngas experiments are conducted at intake temperatures of 250 °C.
• Syngas with lower H2:CO ratio, high moisture and tar contents are preferable.
• For intake conditions, low temperatures and high pressures are preferable.
• Indicated efficiency >33% and IMEP >2.5 bar are achieved.

Syngas, from biomass gasification, needs to be purified of condensible tars before being used as a fuel for spark ignition engines. A novel tar tolerant system is being developed, wherein a (Homogeneous Charge Compression Ignition) HCCI engine is fueled by impure syngas at intake temperatures above the tar dew point, thus avoiding the condensation of tars and its consequent problems. This paper introduces the novel concept and studies the sensitivities of HCCI combustion to key context relevant issues such as the variations in the combustible composition (H2:CO ratio from 30:70 to 55:45%), moisture (upto 12% by volume) and tars (from 3 to 17 g/Nm3) at the intake temperatures of around 250 °C. The effects of intake temperatures (230–270 °C) and pressures (1.0–1.2 bar) are also studied. The experiments are carried out with artificial syngas on a 435 cc mono-cylinder HCCI engine with a compression ratio of 12 and operated at 1500 RPM. Indicated efficiencies about 34% and Indicated Mean Effective Pressures about 2.5 bar were achieved at equivalence ratios between 0.3 and 0.34. In the tested ranges, moisture delayed the combustion while the effect of tars were insignificant.

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