1.

(a)

What is the primary drawback of using a traditional tailpipe-only approach when comparing the CO₂ emissions associated with vehicles which are propelled by internal combustion engines, and those with battery electric propulsion systems.

[3 marks]

(b)

Proposed legislation aims to the reduce average carbon intensity in the UK national electricity network from 162 g CO₂/kWh to 50 g CO₂/kWh. If this new scenario was achieved, how much less time would it take to reach a CO₂ emission break-even point (to the nearest year), when comparing the data for the ICE and BEV vehicles provided below. Provide results for 2, 4, 6, 8 and 10 years after vehicle manufacture. Take the average annual vehicle usage to be equivalent to 11,120 km. Plot your results using the graph paper provided.

Vehicle A (internal combustion engine propulsion system):

• Embedded (manufacture of vehicle): 5,600 kg CO₂ 

• In-service tailpipe emissions 83.5 g CO₂/km Vehicle B (battery electric propulsion system):

• Embedded (manufacture of vehicle including battery): 10,679 kg CO₂ 

• In-service vehicle energy consumption rate 0.137 kWh/km

[17 marks]

2.

(a)

Describe, with the aid of a sketch of the relevant pressure/volume (PV) diagrams of the Otto and the Diesel cycle. Describe the thermodynamic process and corresponding practical process that is assumed to be happening during each phase of the cycle.

[6 marks]

(b)

Describe with the aid of a sketch a pressure/volume (PV) diagram of a typical gasoline engine operating under throttled conditions. Annotate the diagram to show regions of positive work, pumping losses and exhaust blowdown losses

[6 marks]

(c)

Describe how “downsizing” an engine can improve its efficiency at part load operating points.  

[4 marks]

(d)

Why would Hydrogen (H2) and Ammonia (NH3) be considered as alternative fuels for future engines. List at least one of the advantages and one of the disadvantages of both Hydrogen and Ammonia as fuels.

[4 marks]

3.

(a)

The separately excited DC machine was widely used in the railway industry as the traction motor before the technical maturity of power semiconductors. It has a straightforward structure for speed control. Sketch the equivalent circuit of the separately excited DC machine and list the methods of speed control.

[3 marks]

(b)

A separately excited DC machine is rated Trated = 10Nm , nrated =

4500rrm. The armature winding resistance is Ra = 0.4��.  When delivering 1.6kW of mechanical power at 3000 rpm, the armature terminal is connected to a 400V DC power supply. The efficiency of the machine is 80%. Neglecting all losses from field winding, use these conditions to calculate torque and back-emf coefficient of the machine

[9 marks]

(c)

Tesla uses induction machine for their first Model S. Now PM becomes a more popular choice in traction motor than induction machine. Compare the pros and cons between PM and Induction Machine. Sketch three phase inverter driving a star connection stator winding from PM machine.

[4 marks]

(d)

An electric propulsion system is sometimes coupled with a mechanical transmission system to form. the powertrain. The components can be arranged on the chassis in various configurations. List three types of electric powertrain configurations and discuss the principles, advantages, and disadvantages of each.

[4 marks]

4.

(a)

A gearbox is being designed for a new car. The estimated vehicle properties are shown in TABLE Q4-1. A 1.5L engine has already been selected for the vehicle and has the efficiency map as shown in FIGURE Q4-1.

TABLE Q4-1

i) Assuming a flat road and an air density of 1.225kg/m³, calculate the tractive power at the wheels to maintain a steady speed of 110 km/h

[4 marks]

ii) It is desired to cruise at this speed in 5^th gear at an engine speed of 2000rpm. Calculate the power at the engine, and hence the engine torque. Use this to estimate the engine efficiency.

[5 marks]

iii) Calculate the overall gear ratio at these conditions and hence the 5^th gear ratio required.

[3 marks]

(b)

It is decided that the 1.5L engine is not powerful enough for the vehicle, and that a 20kW electric motor will be added to the powertrain between the engine and clutch. What architecture and level of hybridisation is described?

[4 marks]

(c)

Describe 2 benefits and 2 drawbacks of hybridisation.

[4 marks]

5.

Waymo operates fully driverless robotaxis in several major U.S. cities. Since the company received approval to charge for their robotaxi service in 2023, the company is now providing over 150,000 paid rides every week. Waymo’s Chinese rival, Apollo Go, is leading the robotaxi market in China. Since operating commercially in 2022, Apollo Go is now providing 75,000 paid rides every week.

(a) 

Both Waymo and Apollo Go robotaxis are ‘SAE Level 4 automation’.  

• Explain the key features of level 4 automation.  

• Explain why Level 3 automation would not be sufficient for this application.  

• Explain why Level 5 automation is not needed for this application.

[7 marks] 

(b) 

Both Waymo and Apollo Go use a comprehensive sensor suite that includes LiDAR, Radar, HD camera and both are using HD maps. Explain how these technologies work together to enable automated driving.

[7 marks] 

(c)

Even though Waymo and Baidu operates in two very different markets (e.g. normal taxi fares, traffic situation and infrastructure readiness), robotaxi companies such as these two are facing similar challenges. List such challenges in at least three aspects.

[6 marks]