Question

An engine manufacturer wants to develop a gasoline engine that produces 300 hP at 6000 rpm. They can achieve 10 bar BMEP at peak power with a naturally aspirated engine, and 20bar BMEP with a turbocharged engine. Most modern light-duty engines have displacements of ~0.5L per cylinder. Determine the displacement and minimum number of cylinders (rounded to nearest whole number) required to meet these specs for: a. A naturally aspirated engine. b. A turbocharged engine.

Answer 1

a). 5 cylinders

b). 3 cylinders

Step-by-step explanation:

To develop a gasoline engine that produces

Power, P = 300 hp

= 300 x 746 = 223710 watt

at speed, N = 600 rpm = 100 rps

and stroke volume
`$V_s=0.5$` L

=
`$0.5 * 10^(-3)\ m^3$`

a). A naturally aspirated engine

BMEP at peak power = 10 bar

=
`$10 * 10^5\ N/m^2$`

Suction volume, V =
`$V_s * N$`

=
`$0.5 * 10^(-3) * 100 = 0.05\ m^3/s$`

Power produced in one engine cylinder , p = BMEP x V

=
`$10 * 10^5 * 0.05$`

= 50000 watts

No. of cylinders required, n =
`$(P)/(p)$`

=
`$(223710)/(50000)$`

= 4.47

So number of cylinders ≈ 5 nos.

b). A turbo charged engine

BMEP = 20 bar =
`$20 * 10^5\ N/m^2$`

and Volume V =
`$0.05\ m^3 /s$`

Power produced in one engine cylinder, p = BMEP x V

=
`$20* 10^5 * 0.05$`

= 100000 watts

Therefore, number of cylinders, n =
`$(P)/(p)$`

=
`$(223710)/(100000)$`

= 2.23

So number of cylinders ≈ 3 nos.