Thermofluids & Turbomachinery,L6 

Assignment 2023-24 RESIT

IC engine performance characteristics, Combustion chamber design, and Gas exchange process

Background

A single-cylinder 4-stroke SI engine was tested on an engine dynamometer at LSBU. Engine torque, fuel flow, airflow, and exhaust gas temperature were measured at 7 different engine speeds, all full-load (FT).

Note: Use the example dataset below to complete the tasks listed. Specification

TD115 Small Engine Test Bed TD114 Engine Instrumentation Unit TD110 (4-stroke Petrol) IC engine:

Manufacturer                                                             Tecumseh

Capacity (manufacturer data)                                    172cc

Stroke (measured)                                                     49.23mm

Bore (calculated)                                                        66.69mm

Compression ratio (manufacturer data)                      6:1

Results of Performance Test 

Table1 – results of single-cylinder SI engine test at LSBU Fuel SG = 0.74

Fuel CV = 42,000 kJ/kg

Typical Specific Heat of Exhaust Gases: 1 kJ/kgK

Tasks

Unless otherwise stated, equations for calculations should be taken from lecture notes and not supporting documentation from test bed manufacturer.

(1)   Calculate and expand Table1 to include the following performance characteristics:

Power (kW) BMEP (kPa)

Fuel mass flow rate (kg/hr) SFC (g/kWh)

Air volumetric flow rate (m3/hr) Air mass flow rate (kg/hr)

AFR

Volumetric efficiency (%)

Brake thermal efficiency (arbitrary overall efficiency) (%)

Note: For calculation of air volumetric and mass flow rates, use Figure 2.6 Viscous Flow Meter Calibration, and Equation 2-11 from ‘TD110-115_1104 Test Bed and Instrumentation for Small Engines.pdf’

 (Worked calculations for one of the engine speed sites, and a short description and note of key equations must be included in your report) (20 marks)

(2)   Plot on graphs the following performance characteristics vs engine speed (rpm):

Torque (Nm) Power (kW) BMEP (kPa)

Mean piston speed SFC (g/kWh)

AFR & lambda Volumetric efficiency (%)

Brake thermal efficiency (arbitrary overall efficiency) (%) Exhaust temperature (degC)

Graphs must be done in MS EXCEL/ Matlab and included in your report. Provide a concise explanation of each of the trends observed in your graphs of performance characteristics. (20 marks)

(3)   Correct the measured Torque and Power to standard conditions according to the formulae given below. Plot on an additional graph the Corrected and Raw power: Take the measured pressure to be the pressure of dry air, in the absence of humidity data.A single-cylinder 4-stroke SI engine was tested on an engine dynamometer at LSBU. Engine torque, fuel flow, airflow, and exhaust gas temperature were measured at 7 different engine speeds, all full-load (FT).

(Worked calculations for one of the engine speed sites and a short description of equation must be included in your report) (5 marks)

(4)     Choose one test site on which to construct an Energy Balance diagram. Indicate fuel energy input, Brake work output, Heat loss to coolant, Heat loss to exhaust. Comment on your results and compare to published literature.

(Worked calculations, and a short description and note of key equations must be included in your report) (10 marks)

(5)   Discuss briefly the process of ignition and combustion in spark ignition (SI) engines. Show the process on a P-CA (pressure – crank angle) diagram, listing key stages in the process. (10 marks) 

(6)    Intake valve / port flow. The Tecumseh cylinder head consists of 2-valves per cylinder arrangement (see figure-1 below). Following a review of literature, estimate the intake valve size and average flow coefficient. Calculate the mean velocity at the minimum cross section (port area) during the intake stroke. Plot a graph of mean velocity (normalised as Mach no) against engine speed, and comment on the results. (Diagrams, worked calculations, and a short description and note of key equations must be included in your report)

Figure1 - 2-valves per cylinder head (15 marks)