Introduction
What is an engine?
An engine is a related group of parts assembled in a specific order which will convert the chemical energy of the fuel to a useful mechanical power
Fig1 Typical engine construction
Video 1 how engine works

What are the available types of fuel used in road vehicle engines?
In fact there are many types of fuel used in car engines but the most famous fuels are:
Petrol (Gasoline) Engine, Diesel engine and CNG (compressed natural gas) engine
Gasoline and diesel fuels are available in most countries, but CNG is limited for some countries.

What is the difference between previous engine types? Or How to choose the most suitable engine?
You must select the appropriate engine type according to your requirement. In the following section the main differences between Petrol, Diesel and CNG engine will be discussed
POV Petrol diesel CNG
Noise Low relatively high low
Vibration Low High moderate
Fuel Price According to your country regulations
Fuel consumption High Very Low Moderate
Estimated Life (Km) 300000 to 800000 500000 to 1500000 200000 to 500000
Service cost the lowest the highest medium
Performance high power and speed high torque high power and speed

As described in previous comparison, all points of view are available you determine the most appropriate engine to your application

Fuel supply system
After selecting the suitable engine fuel type, you must select the suitable engine equipped with the fuel system. The first established fuel supply system is Mechanical system for both petrol and diesel engines. The carburetor was used to supply petrol fuel to the engine while mechanical fuel injection valve was used to supply diesel fuel.
Since 1950, the fuel supply systems were modified. Today the Electronic fuel injection systems for both petrol and diesel engines.
The electronic fuel supply system advantage:
1-less fuel consumption
2-Best performance
3-less exhaust emissions to match different environment regulations
The ECU (Electronic Control Unite) receives signals from sensors then it calculate the appropriate amount of fuel, the start of injection and also it receive feedback signal to evaluate the decision and modify it if there is any error.
So you must be sure that you buy an electronic control fuel supply system.

What is a turbo or super charge system?
The super or turbo charger system concept is inserting compressed air inside the engine cylinder, so more amount of fuel can be injected resulted in more output power for the same engine capacity. You can compare the car equipped with super or turbo charger with the car without super or turbo charger and select the most appropriate car that suite your requirements.

Valve opening mechanism
The internal combustion engine work with the cycle concept, 4 stroke engines, i.e. the complete cycle is done every 4 strokes. In order to let air and fuel to enter inside the engine and the exhaust gas (after combustion) to get out valves are used to perform this tasks. The valve control mechanism has a great effect on the engine performance. In old models there were 2 valves used for each cylinder, intake and exhaust gas. As technology improved number of valves for each cylinder increase. So when you buy a new car it is necessary to know how many valves for each cylinder and as number of valves increase, the engine performance and efficiency increased.
Also the valve control mechanism is very important, the valve lift (movement) must be adjusted with difference engine operation condition, and this case is not available for conventional valve control mechanism.
Conventional engines control air intake (outside air is filtered then directed to the combustion chambers, naturally or compressed by a direct compressor or a turbo compressor) using a throttle valve. With Valvematic, the volume of air taken in is adjusted by continuously controlling the intake valve lift volume and timing of valve opening and closing, bringing optimal performance based on the engine's operational condition, combining high fuel efficiency with dynamic performance.

The first application of Valvematic will arrive in a new 2.0-litre engine to be introduced soon. This new system further evolves the Toyota petrol engine and improves fuel efficiency by between 5 and 10 per cent (depending on driving conditions), reduces CO2 emissions, boosts power output by at least 10 per cent and enhances throttle response.
So you must be aware to know what is the type of valve control mechanism for the car you want to buy and compare price with expected benefits.

Compression ratio
The engine compression ratio is a very important parameter that determines the overall engine performance. For petrol and CNG engines, the typical compression ratio is 10-16 and for diesel engine more than 18.In most engines the compression ratio is constant but recently a new technology is introduced to change the compression ratio to suit engine operation condition.
This modification is an option because as compression ratio changes, the engine power efficiency and performance changed but this option is expensive and complicated.

What is EGR?
In internal combustion engines, exhaust gas re-circulation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines.
EGR works by recalculating a portion of an engine's exhaust gas back to the engine cylinders. In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.
Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates