MECH9761 Automobile Engine Technology
The Complete Exam Bible · T3 2026MECH9761 Overview
- UNSW Sydney
- Term 3 2026
- Postgraduate engineering
- Mathematical and laboratory analysis
MECH9761 Automobile Engine Technology at UNSW Sydney links thermodynamic models to the hardware and measurements used to understand modern engines. The opening block establishes the four-stroke sequence and the physical differences between spark-ignition and compression-ignition engines.
- Assessment shape Interactive lectures, mid-term test, laboratory report and final exam total the course mark.
- Core method State the boundary, show unit conversion, calculate, then connect the result to an engine mechanism.
- Lab evidence Code, figures, tables and engineering interpretation are all part of the report evidence.
What you get in the full MECH9761 Exam Bible
- 6 chapters, 35 pages — every examinable topic, week by week
- 18 original practice questions, each with a model answer in the Final exam format
- 6 worked examples, solved the way MECH9761 marks
- 12 computed figures, redrawn from the course’s own numbers
- Exam-morning plan for the Final exam (50%) — what to revise last, where marks are lost
Free on this page: assessment table, chapter map, one worked example, key terms, FAQ. The rest is in the full exam bible.
How MECH9761 is assessed
| Component | Weight | Format |
|---|---|---|
| Online interactive lectures | 10% | Assignment; ten interactive modules in the Term 3 teaching plan |
| Mid-term test | 20% | Examination; one hour in the Term 3 teaching material |
| Lab report | 20% | Report; the current handbook groups the laboratory component at this weight |
| Final exam | 50% | Examination; two hours in the Term 3 teaching material |
The current UNSW handbook publishes four rows totalling 100%. The Term 3 lecture deck and laboratory guide describe the 20% laboratory component as 5% attendance and a report scaled to 15%; confirm how the split appears in Moodle. Confirm component-level pass requirements, final question structure and permitted materials in the current official instructions.
Assessment structure
What other students are asking about MECH9761
- Where can I find lecture notes or study guides for MECH9761 at UNSW?
- The MECH9761 study guide in AskSia Library covers Automobile Engine Technology in 6 chapters, with the assessment table, a chapter-by-chapter topic map, key terms and a worked example, free to read on this page.
- Is there a final exam in MECH9761, and how much is it worth?
- Yes. In the offering this AskSia Library guide is built from, Final exam carries 50% of the MECH9761 mark; the full split is Online interactive lectures 10%, Mid-term test 20%, Lab report 20%, Final exam 50%.
- What does MECH9761 cover on otto and diesel cycle efficiency?
- In AskSia Library's MECH9761 guide, the Otto and Diesel Cycle Efficiency chapter explains pressure-volume loops, compression ratio, cutoff ratio and theoretical efficiency.
- What does MECH9761 cover on combustion thermochemistry and equilibrium?
- In AskSia Library's MECH9761 guide, the Combustion Thermochemistry and Equilibrium chapter explains stoichiometry, flame temperature, mixture strength, dissociation and Gibbs equilibrium.
- What does MECH9761 cover on engine performance and mean effective pressure?
- In AskSia Library's MECH9761 guide, the Engine Performance and Mean Effective Pressure chapter explains torque, power, fuel efficiency, pressure-volume work and the MEP loss ledger.
Current MECH9761 dates
| Date | Item | Control |
|---|---|---|
| 2026-11-05 | Laboratory report due | 2 pm, at the start of the Week 8 demonstration |
The 2026 T3 laboratory guide publishes this deadline; confirm any update on Moodle.
What MECH9761 covers
Begin with four-stroke architecture and ideal Otto and Diesel cycles, then connect combustion chemistry to performance measures, spark-ignition controls and laboratory pressure analysis.
Engine Architecture and Cycle Comparisons
Four-stroke operation, spark ignition, compression ignition and energy boundariesThis chapter establishes the four-stroke sequence and the energy boundary of an internal-combustion engine, then compares spark-ignition and compression-ignition hardware.
- Intake, compression, expansion and exhaust as one repeating cycle
- Internal combustion as direct energy conversion within the working fluid
- Spark ignition compared with compression ignition
- Throttle control compared with fuel-quantity control
- Stored energy, conversion efficiency and idealised driving range
- Model boundaries in electric and liquid-fuel comparisons
Otto and Diesel Cycle Efficiency
Pressure-volume loops, compression ratio, cutoff ratio and theoretical efficiencyThis chapter reads the Otto and Diesel air-standard cycles through their pressure-volume paths and efficiency equations. The Otto model adds heat at constant volume; the Diesel model uses constant-pressure heat addition and a cutoff ratio.
- Pressure-volume loop area as ideal net cycle work
- Constant-volume heat addition in the Otto model
- Constant-pressure heat addition in the Diesel model
- Compression ratio and specific-heat ratio effects
- Diesel cutoff ratio and its efficiency penalty
- Air-standard ceilings compared with brake efficiency
Combustion Thermochemistry and Equilibrium
Stoichiometry, flame temperature, mixture strength, dissociation and Gibbs equilibriumThis chapter builds combustion calculations in a strict order: balance atoms, calculate the stoichiometric air-fuel ratio, classify the actual mixture, then apply energy or equilibrium relations.
- Complete hydrocarbon combustion with oxygen and inert nitrogen
- Reaction enthalpy from formation enthalpies
- Adiabatic flame temperature through an enthalpy balance
- Stoichiometric air-fuel ratio for a general hydrocarbon
- Lambda and phi classifications for lean and rich mixtures
- Dissociation, Gibbs free energy and water-gas-shift equilibrium
Engine Performance and Mean Effective Pressure
Torque, power, fuel efficiency, pressure-volume work and the MEP loss ledgerThis chapter turns engine operating data into comparable performance measures. Torque and speed determine power; fuel flow and lower heating value determine conversion efficiency.
- Brake power as the product of angular speed and torque
- High-speed torque decline through reduced volumetric efficiency
- Fuel-conversion efficiency and specific fuel consumption
- Cylinder geometry and pressure-volume integration
- Brake, gross indicated and net indicated MEP
- Pumping and friction losses in the MEP identity
Spark Ignition Combustion and Air Management
Injection, boost, valve timing, tumble, ignition and flame propagationThis chapter follows the causal chain of spark-ignition combustion: mixture preparation, ignition and turbulent flame propagation.
- Port injection compared with direct injection
- Charge cooling, atomisation, wall wetting and particulates
- Turbochargers, superchargers and volumetric efficiency
- Variable intake-valve timing and trapped charge
- Tumble breakdown into turbulence near ignition
- Spark timing, flame propagation and best torque
Cylinder Pressure Analysis and Lab Reporting
Pressure reduction, apparent heat release, combustion phasing and report evidenceThis chapter turns laboratory measurements into reproducible engineering evidence. Pressure is aligned with volume calculated from geometry, integrated to obtain work and normalised to IMEP.
- Sensor zeroing and aligned pressure-crank-angle data
- Cylinder volume from engine geometry
- Pressure-volume integration and IMEP
- Apparent heat-release rate under a constant gamma assumption
- Start of combustion and cumulative heat-release phasing
- Spark-timing and diesel-load comparisons
It then develops the ideal Otto and Diesel cycles, showing how compression ratio, cutoff ratio and the heat-addition path affect theoretical efficiency. Combustion thermochemistry adds atom balances, formation enthalpy, adiabatic flame temperature, air-fuel ratio, equivalence ratio and chemical equilibrium.
Performance analysis connects torque and speed to power, separates brake and indicated output, and uses mean effective pressure to compare engines independently of displacement. The spark-ignition material follows mixture preparation, injection choice, turbocharging, variable valve timing, tumble, spark timing and flame propagation.
The laboratory chapter then turns measured cylinder pressure and calculated volume into work, IMEP, apparent heat-release rate and combustion-phasing metrics. Assessment in the current UNSW handbook totals 100% across online interactive lectures, a mid-term test, a lab report and a final exam. The Term 3 teaching material states that the final is two hours and carries half of the course mark.
The laboratory guide requires completed Cantera and MATLAB work, numbered figures with labelled units, summary tables and engineering explanations that distinguish observation from inference. The guide uses original worked numbers while preserving the methods demonstrated in the university materials, so revision focuses on setup, units, calculation and physical interpretation rather than memorising isolated answers.
Worked example · free
Convert brake power and speed into torque
- +1Convert speed to revolutions per second: N = 3000/60 = 50 rev/s.
- +1Use P = 2 pi N T and rearrange to T = P/(2 pi N).
- +1Substitute SI values: T = 96000/[2 pi(50)] = 305.6 N m.
- +1At higher speed, reduced induction time can lower volumetric efficiency and torque.
Key terms
- Brake power
- Brake power is the usable shaft work rate measured with a dynamometer.
- Compression ratio
- Compression ratio is maximum cylinder volume divided by minimum cylinder volume.
- Cutoff ratio
- Cutoff ratio describes the volume change during constant-pressure heat addition in the ideal Diesel cycle.
- Equivalence ratio
- Equivalence ratio is stoichiometric air-fuel ratio divided by actual air-fuel ratio.
- Air-excess ratio
- Air-excess ratio is actual air-fuel ratio divided by its stoichiometric value.
- Adiabatic flame temperature
- Adiabatic flame temperature is the product temperature predicted when combustion loses no heat across the boundary.
- Mean effective pressure
- Mean effective pressure is cycle work divided by displacement volume.
- Pumping loss
- Pumping loss is gas-exchange work required to move charge through intake and exhaust restrictions.
- Volumetric efficiency
- Volumetric efficiency measures cylinder filling relative to a reference intake density and displacement.
- Tumble flow
- Tumble flow is organised in-cylinder motion that can break down into turbulence near ignition.
- Apparent heat release
- Apparent heat release is combustion-energy release inferred from measured pressure and calculated volume under model assumptions.
- Combustion phasing
- Combustion phasing locates heat-release milestones such as CA10, CA50 and CA90 against crank angle.
MECH9761 FAQ
How hard is Automobile Engine Technology?
The challenge is switching cleanly between thermodynamic models, chemistry, hardware and measured data. Most calculations use a compact set of relationships, but units and model boundaries matter. Regularly rework cycle efficiency, mixture classification, torque-power and MEP identities, then add one physical interpretation sentence to each result.
How much is the final exam worth?
The current UNSW handbook assigns 50% to the Final exam, and the Term 3 teaching material states a two-hour duration. Confirm the current question structure, venue, start time and permitted aids on Moodle and the UNSW examination timetable.
How is the laboratory component assessed?
The current handbook groups Lab report at 20%. The Term 3 lecture deck and laboratory guide describe that component operationally as 5% attendance plus a report scaled to 15%. The report tasks are marked out of 50 and require completed code, figures, tables, calculations and engineering explanations.
Which formulas should I know first?
Start with Otto and Diesel ideal-cycle efficiency, P = 2 pi N T, fuel-conversion efficiency, the MEP loss identities, stoichiometric air-fuel ratio, lambda and phi, and work as the integral of p dV. Pair every formula with its boundary, unit conversion and one physical check.
What does the pressure-analysis laboratory test?
It tests whether you can convert measured pressure and engine geometry into pressure-volume work, IMEP, apparent heat-release rate and combustion-phasing metrics. The report also tests data presentation: figures need numbered captions, labelled axes with units, tabled results and discussion that separates direct observations from engineering inferences.
Where should I get revision practice?
Use the official demonstration questions and Moodle activities as the primary course practice, then use the original questions in this guide to vary numbers and operating conditions. Treat the practice here as method rehearsal and follow the current official assessment instructions.
Questions students ask in each MECH9761 chapter
- Is combustion a separate engine stroke?
- Combustion is not a fifth piston stroke. It is a rapid chemical process placed around the end of compression and the start of expansion. The four piston motions remain intake, compression, expansion and exhaust. Calling combustion a stroke hides the difference between piston kinematics and heat-release timing. Chapter 01 · Engine Architecture and Cycle Comparisons
- Why is the ideal Otto cycle better at one fixed compression ratio?
- At a cutoff ratio above one, the Diesel-cycle correction factor increases the subtracted term in its efficiency equation. With compression ratio and specific-heat ratio fixed, that makes the ideal Diesel result lower than the Otto result. This is a model comparison, not a production-engine fuel-economy claim. Chapter 02 · Otto and Diesel Cycle Efficiency
- Why must atoms be balanced before the energy equation?
- Species coefficients are the mole numbers multiplying formation and sensible enthalpies. If the atom balance is wrong, the energy sum cannot conserve mass and its temperature or heat result is meaningless. Balance carbon, hydrogen and oxygen first, then bring those coefficients into the enthalpy equation. Chapter 03 · Combustion Thermochemistry and Equilibrium
- Why can power rise while torque is falling?
- Power equals torque multiplied by angular speed. After torque passes its peak and begins to decline, rising speed can still more than offset that fall, so power continues upward. Eventually worsening cylinder filling or other limits reduce torque enough that power also reaches a peak and falls. Chapter 04 · Engine Performance and Mean Effective Pressure
- Why can direct injection increase particulate emissions?
- Direct delivery shortens the available mixing time and can create locally rich pockets. Spray impingement may wet the piston or liner and form a liquid pool that burns incompletely. Higher injection pressure improves atomisation but does not remove the need for careful targeting, timing and wall-temperature control. Chapter 05 · Spark Ignition Combustion and Air Management
- Why is apparent heat release called apparent?
- It is inferred from pressure and volume through a simplified first-law model. Wall heat transfer, crevice flows, mass exchange, variable properties and sensor effects are not all resolved directly, so the calculated curve represents an apparent release under stated assumptions rather than a direct chemical measurement. Chapter 06 · Cylinder Pressure Analysis and Lab Reporting
How to study for the exam
Build revision around causal chains, not isolated definitions. First draw the four-stroke sequence and label the intake charge, compression process, ignition trigger, expansion work and exhaust path for both spark and compression ignition. Next derive the ideal-cycle formulas and practise fixed-ratio comparisons before bringing back real compression ratios and losses.
For thermochemistry, never skip atom balance: calculate oxygen demand, carry the nitrogen, convert moles to mass, classify lambda and phi, then decide whether complete products are defensible. For performance, convert rpm before using the power-torque relationship and rebuild the gross, net and brake MEP ledger from measurement locations.
For spark-ignition controls, explain each technology as a chain from hardware to charge state, flame behaviour, work and emissions. Finally, rehearse the laboratory workflow from sensor zeroing to volume, p dV integration, IMEP, apparent heat release and CA10, CA50 and CA90. Make every practice answer end with units, a sign check and one sentence stating the physical mechanism and the model limitation.
