IC Engines

Question 1

TDC

Answer 1

Top Dead Centre. Highest Point of engine cylinder

Question 2

BDC

Answer 2

Bottom Dead Centre. Point at the bottom of the cylinder motion where it stops and changes direction

Question 3

Four stroke Cycle stages

Answer 3

1. Inlet 2. Compression 3. Expansion (Power) 4. Exhaust

Question 4

Engine Torque Delivery

Answer 4

Highly irregular. Maximum Torque in the Power (Expansion) Stroke. ICE use multiple cylinders to smooth the engine torques.

Question 5

Flywheel use

Answer 5

Large disk at the end of the crankshaft to add inertia to the shaft to smooth the torque

Question 6

Combustion Equation

Answer 6

CxHy + O2 + (79/21) N2 > CO2 + H2O + N2 in a perfect combustion - in reality also get Soot (Carbon particles); NOx (Nitrous oxides; pollutant and greenhouse gas); HC (Unburnt fuel) and; CO (Carbon Monoxide)

Question 7

Pre-mixing the air with the fuel

Answer 7

Flame burns blue, no orange or soot formation

Question 8

Air/Fuel Ratio (AFR) Equation

Answer 8

ma / mf = .ma / .mf ( dot indicates mass flow

Question 9

Stoichiometric

Answer 9

Correct AFR to perfectly convert fuel to CO2

Question 10

lambda equation

Answer 10

lambda = AFRactual / AFRstoich = 1/phi

Question 11

SI (petrol) engines lambda value

Answer 11

Usually run at lambda = 1 (Stoichiometric) at all loads
AFR = 14.5 - 14.7

Question 12

CI (diesel) engines AFR

Answer 12

Usually run lean on fuel but move towards lambda = 1 at full load
AFR = 15-70

Question 13

AFR for best power output

Answer 13

approx 12-13. fuel rich

Question 14

AFR for emmisions targets

Answer 14

14.5-14.7. SI runs here as 3 way catalyst can brake up all of the emmisions

Question 15

Peak NOx AFR

Answer 15

Little over 16. This is due peak temperatures at slightly lean fuel mix

Question 16

SI combustion

Answer 16

Fireball grows from spark ignition. The outer surface forms some NOx but less soot

Question 17

CI combustion

Answer 17

Fuel auto ignites after injection and sufficient time to mix with air. Local ignition occurs at the ends of each injected spray. Irregular fuel mixing leads to high NOx and Soot. Less unburned HC and CO

Question 18

HCCI combustion

Answer 18

Fuel is premixed with hotter gases. Multiple ignition sites after compression but prior burned gases lead to a cooler combustion so zero NOx and zero soot. Similar HC and CO exhaust to gasoline

Question 19

SI

Answer 19

Spark Ignition - Petrol

Question 20

CI

Answer 20

Compression Ignition - Diesel

Question 21

HCCI

Answer 21

Homogeneous Charge Compression Ignition - Petrol

Question 22

Benefits of Diesel

Answer 22

Much greater Fuel Economy and reduced CO2 emissions. As well as reduced HC and CO emissions

Question 23

Downsides of Diesel

Answer 23

High Soot and particulates - increased cost. Increased NOx emmisions

Question 24

HCCI benefits

Answer 24

Much lower NOx emissions and reduced CO2 and improved fuel economy

Question 25

HCCI downsides

Answer 25

Greater cost and reduced combustion control

Question 26

Diesel Fuel economy reasoning

Answer 26

Higher compression ratio and therefore greater expansion ration which means more work is obtained during the power stroke
Do not use a throttle so there is no pumping losses under partial load conditions
Use high amounts of EGR

Question 27

EGR

Answer 27

Exhaust Gas Recirculation. Is used to reduce peak combustion temperatures and reduce NOx emissions

Question 28

Road transport CO2 emmisions by transport type

Answer 28

32% petrol cars
30% diesel cars
18% HGV
16% vans
3% buses
1% other
22% of UK total CO2 emissions

Question 29

Crude Oil

Answer 29

Main products of Crude oil distillation are gasoline and diesel.

Question 30

Diesel market share in the EU

Answer 30

Between 2005 and 2015 Diesel cars made up over 50% of new passenger cars in the EU. Now on the decline

Question 31

Diesel Popularity

Answer 31

Excelent Fuel Economy - linked to tax incentives
Fun to drive due to low speed torque

Question 32

Diesel Combustion Dirtiness

Answer 32

Main combustion occurs near the TDC and is contained within the piston bowl
Fuel injector typically has 6 or more injector orifices so multiple flame zones

Question 33

Diesel after emissions treatment

Answer 33

1. Oxidation catalyst
2. Passive Particulate Filter to oxidise particulates
3. NO2 decomposition catalyst
   NOx trap has been replaced with a selective catalytic reduction due to VW scandal in 2015

Question 34

2017 Ban

Answer 34

New sales of conventional ICE vehicles banned from 2040. Hybrids currently not included