# What factors affect engine compression ratio?

## What factors affect engine compression ratio?

Reciprocating Internal Combustion Engines The pressure and temperature at the end of compression will be affected by the compression ratio, with a higher compression ratio increasing both these parameters.

## What factor limits the compression ratio in SI and CI engine?

Since CI engines rely upon fuel injected into the cylinder and the mixing of this fuel with the air, engine knock is avoided. Engine knock is one of the primary limitations to higher compression ratio in SI engines. The second factor is the eliminated need for throttling the engine to control power output.

What is the compression ratio in SI engine?

In the SI engine, fuel is mixed with air, broken up into a mist, and partially vaporized. The compression ratio varies from 4:1 to 8:1, and the air–fuel mixture ratio varies from 10:1 to 20:1. The four strokes of a petrol engine sucking fuel–air mixture are shown in Fig. 2.2.

### How does compression ratio affect the engine performance?

The thermal efficiency increases and the brake specific fuel consumption decreases with the increase of compression ratio. The higher compression ratio results in higher in-cylinder pressure and higher heat release rate as well as lower ignition delay.

### When we increase the compression ratio in SI engine the knocking tendency?

Solution(By Examveda Team) In SI engine, knocking tendency increases with increase in compression ratio. In CI engine, knocking tendency decreases with increase in compression ratio. If compression ratio is low in CI engine, there will not be enough temperature generation for ignition of the fuel air mixture.

What is the compression ratio in SI engine Mcq?

The compression ratio for petrol engines is: 15 to 20.

#### Why SI engines Cannot use higher compression ratios?

Compression ratios in SI engines is limited because of the occurance of ignition knock.

#### What causes high compression in an engine?

If the compression increases, you can tell there is a piston or piston ring problem. While the pistons may encounter damage from overheating and fail to seal in the gas, they are still intact. Worn rings can cause low compression in one or all cylinders.

How do you increase compression ratio in an engine?

Higher compression is normally achieved in a few ways:

1. By changing the flat-top pistons to high compression ones that curve upward to result in a higher compression ratio. However, since the air and fuel are both more highly compressed, there will be more heat.
2. Turbocharging.
3. Supercharging.

## What is highest useful compression ratio?

Highest useful compression ratio (HUCR) is the highest compression ratio at which the

• A. Engine can run.
• Engine gives maximum output.
• Engine is most efficient.
• Fuel can be used in a test engine without knocking.

## Which cycle is mostly used in high compression engines?

In such a case, a better approach for modelling the situation will be to assume heat addition initially at constant volume and then at constant pressure. That is why dual combustion cycle is used.

Which of the following factors affect combustion in CI engine?

In CI engine, combustion occurs by the high temperature produced by the compression of the air. Explanation: None. 2. In the CI engine, the intake is air alone and the fuel is injected at high pressure in the form of fine droplets at the start of compression.

### What is the effect of compression ratio on engine knock?

Increasing the compression ratio increases both the temperature and pressure (density of the unburned mixture). Increase in temperature reduces the delay period of the end gas which in turn increases the tendency to knock. It also increases both temperature and density, which increase the knocking tendency of engine

### What are the engine parameters that affect knocking?

The various engine variables affecting knocking can be classified as: Increasing the temperature of the unburned mixture increase the possibility of knock in the SI engine we shall now discuss the effect of following engine parameters on the temperature of the unburned mixture: i. Raising the Compression Ratio

How does the flame speed increase with increase in compression ratio?

At high compression ratios both pressure and temperature of the air fuel mixture would increase. These two conditions favour the flame speed. Thus flame speed increases with increase in compression ratio. Increase of residual gases in the combustion chamber would reduce the flame speed.

#### What are the factors affecting the performance of an engine?

Engine size: For larger engine size the flame travel distance will be longer and hence knocking chances are high, because of this reason SI engine sizes are generally limited. There are two hot spot zone in SI engines. ie., spark plug & exhaust valve.