What causes high NOx readings?
High NOx levels are normally caused by high combustion temperatures and pressures, slightly lean AFR, and excessively advanced ignition timing.
What is HC emission?
11.4. HYDROCARBON EMISSIONS. Hydrocarbons, or more appropriately organic emissions, are the consequence of incomplete combustion of the hydrocarbon fuel. The level of unburned hydrocarbons (HC) in the exhaust gases of gasoline fueled spark-ignition engines is typically 1 to 2% of the fuel: in diesels it is much less.
What is NOx in diesel engines?
In the exhaust of internal combustion engines, NOx refers to a class of compounds called nitrogen oxides. In DI diesel engine exhaust, nitric oxide (NO) is usually the most abundant nitrogen oxide and constitutes more than 70-90% of total NOx at engine-out conditions.
What is PM NOx trade off?
NOx-PM trade-off. Heavy-duty diesel engine technology from the 1990s. Within each engine technology group, lower NOx emissions can be achieved at the cost of higher PM emissions.
What does HC ppm mean on emissions test?
Find “HC PPM” within the tailpipe section. You read this as hydrocarbon parts per million, and it means the number of hydrocarbon molecules for every million molecules emitted through the exhaust.
How do you reduce HC emissions?
On a precomputer carbureted car, one way to get under the HC and CO limits is to retard the ignition timing. This will slow the idle and provide a longer, hotter burn. Then, bring the idle speed back up to specs with the throttle stop screw or idle stop solenoid, which will admit more air.
What is HC in gas?
Hydrocarbons (HC) Is raw gasoline or gasoline that has not burned. Associated with incomplete combustion. Combines with NOx and sunlight to form photochemical smog. Carbon Monoxide (CO) Is partially burned fuel known as a rich indicator.
What does high HC ppm mean?
A high HC reading means the test found high HC (hydrocarbons) in your emissions. In other words, too much gas is left in the exhaust after combustion.
How is HC formed?
Surface/volume (s/v) ratio: A small engine of low displacement volume will have higher surface to volume ratio which is responsible for formation of hydrocarbon (HC). Experimental results have shown the low C.R., lower bore to stroke ratio and larger displacement lowers the s/v ratio, hence, reduce HC emission.
Why do diesel engines produce NOx?
Q. Why are NOx gases produced? High temperature combustion of fuels where the temperature is hot enough (above about 1300°C/ 2370°F) to oxidise some of the nitrogen in air to NOx gases. This includes burning hydrogen, as it burns at a very high temperature. Comments on diesel engines are shown below.
How do diesel engines reduce NOx emissions?
NOx emission can be reduced by primary methods such as retard injection, fuel nozzle modification, change of compression ratio, water direct injection, water emulsification, exhaust gas recirculation (EGR) and secondary method such as selective catalytic reduction (SCR).
What is NOx and PM?
Certain harmful air pollutants are emitted directly from vehicles, such as ‘primary’ particulate matter (PM) and nitrogen oxides (NOX). Others, such as ozone and ‘secondary’ PM, form in the atmosphere after emissions of precursor pollutants, including NOX and volatile organic compounds.
What are HC and NOx and why are they important?
The HC and NOx are what it takes to create smog, so if we prevent them from coming out of the tailpipe, we can cut down on the smog. In any diagnosis of emission or driveability related concern, ask yourself the following questions:
What is NOx and why does it matter?
It is a strong oxidizing agent and plays a major role in the atmospheric reactions with volatile organic compounds (VOC) that produce ozone (smog) on hot summer days. The pie chart below shows how NOx emissions in New England were distributed among the various sectors in 2002.
What causes high NOx and HC in a gas analyzer?
If the vehicle is not running rich, the gas analyzer will read high HC, low CO, high O2, low CO2, and high NOx. The reason for the high O2 is that the carbon will assimilate a lean ignition misfire.
What causes high NOx in a gas valve?
As a result, the valve and its seat will rise in temperature, causing preignition. This will result in high HC, low CO, high O2, low CO2, and high NOx. So as you can see, excessive NOx is caused by high internal temperatures.