Questions: A compression ignition engine when tested gave an indicator card having area 2950 mm^2 and length 68 mm. The calibration factor was 0.2 bar / mm. The mechanical efficiency of the engine was 80%. Calculate the IMEP and the BMEP.

A compression ignition engine when tested gave an indicator card having area 2950 mm^2 and length 68 mm. The calibration factor was 0.2 bar / mm. The mechanical efficiency of the engine was 80%.

Calculate the IMEP and the BMEP.

Transcript text: A compression ignition engine when tested gave an indicator card having area $2950 \mathrm{~mm}^{2}$ and length 68 mm . The calibration factor was $0.2 \mathrm{bar} / \mathrm{mm}$. The mechanical efficiency of the engine was $80 \%$. Calculate the IMEP and the BMEP.

Solution

Solution Steps

Step 1: Calculate the Average Height of the Indicator Card

To find the average height of the indicator card, we divide the area of the indicator card by its length: \[ \text{Average Height} = \frac{\text{Area}}{\text{Length}} = \frac{2950 \, \text{mm}^2}{68 \, \text{mm}} = 43.3824 \, \text{mm} \]

Step 2: Calculate the Indicated Mean Effective Pressure (IMEP)

The IMEP is calculated by multiplying the average height by the calibration factor: \[ \text{IMEP} = \text{Average Height} \times \text{Calibration Factor} = 43.3824 \, \text{mm} \times 0.2 \, \text{bar/mm} = 8.6765 \, \text{bar} \] Rounding to four significant digits: \[ \boxed{\text{IMEP} = 8.676 \, \text{bar}} \]

Step 3: Calculate the Brake Mean Effective Pressure (BMEP)

The BMEP is calculated by multiplying the IMEP by the mechanical efficiency: \[ \text{BMEP} = \text{IMEP} \times \text{Mechanical Efficiency} = 8.676 \, \text{bar} \times 0.80 = 6.9408 \, \text{bar} \] Rounding to four significant digits: \[ \boxed{\text{BMEP} = 6.941 \, \text{bar}} \]