increases. The increase in power output is a result of several different
combustion variables are affected by water injection. Water injection
leads to increase in both ignition delay period and combustion period
due to slower burn rates [2]. Thus, the charge requires less compression
work than the LPG alone due to the longer ignition delay during the
compression stroke. This helps to reach the peak pressure after TDC to
produce more power output during the expansion stroke.
The variation of brake specific fuel consumption with engine
speed for the different water to fuel mass ratio is shown in figure 3.
The BSFC decreases to a minimum as the engine speed increases at
low engine speed, and then begins to increase at high speeds. At low
speeds, the longer time per cycle allows more heat loss and lower
combustion efficiency resulting in fuel consumption goes up for the
power produced. Fuel consumption increases at high speed because of
greater friction losses. Figure 3 shows that as the water to fuel mass ratio
increases, the BSFC decreases. The minimum BSFC value occurs when
the water to fuel mass ratio is 0.5. Injected water leads to burn more fuel
due to longer ignition delay and suppression of thermal dissociation
due to lower mean cylinder temperature. Increase in specific heat and
molecular weight of the burned gas and the heat absorption of water
during the intake stroke yielded to a decrease in the mean cylinder
temperature.
Figure 5 shows the effect of water addition on the brake thermal
efficiency. As expected, the maximum increase in brake thermal
efficiency occurs when 0.5 of water to fuel mass ratio is occurred, and
this is due to the fact that the BSFC is minimum at the same time, as