The role of biomass energy is becoming more and more important
in renewable energy. As biomass energy utilization has the problems
of collection and transportation. A small-scale dispersed power
source is required. Biomass gasification CHP (combined heat and
power) system converting biomass energy into gas for CHP at high
temperature is one of the most effective solutions because of its
high energy conversion efficiency.
Dual fuel engine which can ignite low calorie biomass
gasification gas by injected light oil is suitable for woody
biomass gasification gas of changing calorie and amount. The effect
of gas ratio which is defined as gas energy ratio in total inlet
energy, injection timing, throttling and gas composition on the
performance and exhaust emission of dual fuel engine was
investigated by using 2 kinds of model gas which consists of H₂,
CO, CH₄, CO₂ and N₂. As gas ratio of low calorie gas increases, NOx
and thermal efficiency decrease but CO and THC increase. At 58% gas
ratio (BMEP = 0.24 MPa) advanced injection timing can improve
thermal efficiency and decrease THC and CO. When throttling was
used at light load, thermal efficiency can be improved. But,
because at high load thermal efficiency is highest and NOx, Sd
(Smoke density) are lowest at WOT, throttle should be wide open. As
first model gas has no CH₄ and high level of CO and H₂, exhaust
emission of first model gas has low THC and high CO.
The dual fuel engine has optimized the injection timing and has
installed an oxidation catalyst to reduce CO. The dual fuel engine
runs by using gas from the biomass gasification CHP system of
downdraft type. The thermal efficiency is achieved over 35% and CO
emission level was less than 100 ppm. Under over 70% gas ratio
condition, NOx emission level is less than 300 ppm in 0% O₂.