Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain Variable Valve Timing (VVT) and its impact.
• Describe the principles and advantages of Gasoline Direct Injection (GDI).
• Compare and contrast turbocharging and supercharging.
• Analyze the role of advanced Engine Control Units (ECUs).

Lesson summary

This week, we delve into the fascinating world of advanced engine technology and its impact on performance. Understanding these advanced concepts is crucial for any aspiring Mechanical Technologist in South Africa. The South African automotive industry, while facing challenges, remains a significant employer and contributor to the economy. New technologies are constantly being introduced in vehicles manufactured and serviced here, demanding skilled technicians who can diagnose, repair, and even improve engine performance.

Lesson notes

2.1 Variable Valve Timing (VVT) VVT systems allow the engine to optimize valve timing based on engine speed and load. Traditional engines have fixed valve timing, a compromise for different operating conditions. VVT overcomes this limitation by adjusting the intake and/or exhaust valve timing.

How it Works: VVT systems typically use hydraulically actuated cam phasers that rotate the camshaft relative to the crankshaft. The ECU controls these phasers based on sensor inputs like engine speed, throttle position, and coolant temperature. This adjustment can alter valve overlap (the period when both intake and exhaust valves are open) and valve duration (the amount of time the valves are open).

Benefits: Improved Fuel Efficiency: Optimizing valve timing at lower engine speeds can reduce pumping losses and improve fuel economy.

Increased Power and Torque: At higher engine speeds, VVT can increase valve overlap, allowing for better cylinder filling and improved power output.

Reduced Emissions: VVT can help optimize combustion, leading to lower emissions of harmful pollutants.

Types of VVT: Cam Phasers: The most common type, rotating the camshaft to adjust timing.

Cam Profile Switching: Uses different cam lobes to change valve lift and duration. (More complex)

South African Context: Many modern vehicles sold in South Africa, from budget cars to luxury SUVs, utilize VVT to meet fuel efficiency and emissions standards. Mechanics must understand VVT to diagnose and repair engine performance issues related to valve timing. 2.2 Gasoline Direct Injection (GDI) GDI is a fuel injection system that injects fuel directly into the combustion chamber, rather than into the intake manifold.

How it Works: GDI systems use high-pressure fuel pumps and injectors to deliver fuel directly into the cylinder. This allows for more precise fuel metering and improved combustion control.

Advantages: Improved Fuel Efficiency: Direct injection allows for leaner air-fuel mixtures, leading to better fuel economy.

Increased Power: More precise fuel metering and improved combustion result in higher power output.

Reduced Emissions: GDI can reduce emissions, particularly during cold starts.

Cooling Effect: As fuel enters the cylinder it absorbs heat, reducing the cylinder temperature and allowing for higher compression ratios to be used, further improving efficiency and power.

Disadvantages: Carbon Buildup: A common issue with GDI engines is carbon buildup on the intake valves, as there is no fuel washing over them to clean them. This requires periodic cleaning.

Higher Fuel System Pressure: GDI systems require high-pressure fuel pumps, making them more complex and potentially more expensive to maintain.

South African Context: GDI is becoming increasingly prevalent in new petrol-powered vehicles sold in South Africa. Technicians need to be trained to diagnose and repair GDI systems, including addressing carbon buildup issues. 2.3 Forced Induction (Turbocharging and Supercharging) Forced induction involves forcing more air into the engine's cylinders than it could naturally aspirate. This increases the amount of fuel that can be burned, resulting in higher power output.

Turbocharging: Uses exhaust gases to spin a turbine, which in turn drives a compressor that forces air into the engine.

Advantages: More efficient as it utilizes waste energy (exhaust gases).

Disadvantages: Turbo lag (a delay in power delivery due to the time it takes for the turbo to spool up).

Supercharging: Mechanically driven by the engine's crankshaft via a belt.

Advantages: Instant boost and no turbo lag.

Disadvantages: Less efficient as it consumes engine power to operate.

Comparison Table: | Feature | Turbocharging | Supercharging | |----------------|------------------------------------------|------------------------------------------| | Power Source | Exhaust Gases | Engine Crankshaft | | Efficiency | Higher | Lower | | Lag | Present (Turbo Lag) | Minimal/None | | Installation | More complex (plumbing, cooling) | Simpler | | Boost at Idle | Little to None | Some boost even at Idle | South African Context: Forced induction is commonly used in performance vehicles and increasingly in smaller, fuel-efficient engines to provide adequate power. Turbocharged diesel engines are also prevalent in commercial vehicles and bakkies popular in South Africa. 2.4 Advanced Engine Control Units (ECUs) ECUs are sophisticated computers that control various aspects of engine operation, including fuel injection, ignition timing, and valve timing (in VVT systems).

How they Work: ECUs receive inputs from numerous sensors throughout the engine and vehicle, such as engine speed, load, temperature, and oxygen levels in the exhaust. Based on these inputs, the ECU calculates the optimal settings for fuel injection, ignition timing, and other parameters to achieve the desired performance, fuel economy, and emissions.

Functions: Fuel Injection Control: Determines the amount and timing of fuel injection.