What is constant Volume sampling?

Constant Volume Sampling. The Constant Volume Sampling (CVS) method has been adopted by most countries for regulatory exhaust emission testing. In the CVS method, the exhaust gases are diluted with air to maintain a constant total flow rate (air + exhaust) under all running conditions.

What is dilution tunnel?

To measure PM emissions during simulated driving conditions in the laboratory, a dilution tunnel is used. Thus, high-speed measurement and control of the dilution air flow is required for the partial-flow dilution tunnel if it is to operate under transient test cycle.

Why is dilution important in sampling of PM from a source?

Dilution sampling has a number of advantages, including source emissions that are measured under conditions simulating stack gas entry and mixing in the ambient atmosphere. This is particularly important for characterizing the semivolatile species in effluents as a part of particulate emissions.

What is exhaust gas dilution?

Exhaust gas dilution mainly occurs during idling and is insignificant during the other two ranges. The fresh charge and the exhaust gas in the cylinder mix up to reduce the air fuel ratio significantly. This results in poor combustion and as a result, a loss of power.

What are the requirements for exhaust gas sampling?

The sampling requirements for particle and gas species measurement are somewhat different. For gas sampling it is of crucial importance that no chemical reactions take place in the sampling train. This means that inert materials have to be used for all parts coming in contact with the exhaust gas.

How is exhaust gas sample used for transient testing?

partial flow dilution system. In the full flow system, the entire exhaust gas stream produced by the engine is mixed with air. In partial flow systems, a sample of gas is drawn from the raw exhaust and diluted with air. Both techniques were shown to be suitable not only for steady-state, but also for transient testing [1039].

What kind of testing is done for CVS emissions?

The gaseous emissions sampling and analysis is incorporated, including analysis of CO (low), CO (high), CO2, NOx, THC, and CH4. The on-site chemistry laboratory provides chemical speciation testing of the dilute exhaust. Automated calibrations, including linearity, interference, and converter checks, ensure maximum productivity of the bench.

What kind of dilution is used for exhaust gas testing?

Exhaust gas dilution can be performed either in a full flow dilution tunnel, such as the CVS system that is commonly used for regulatory testing, or in a partial flow dilution system. The dilution step is very important to obtain representative measurement; sample losses or changes in sample properties can cause significant errors.