How to Reduce Emissions From Gas Engines

Going green is about reducing consumption and treating what's left.

Engine emissions are a complex but well-researched field, and involve all aspects of powertrain engineering from the air filter to the tailpipe. While the average engineer's inherent tendency might be to focus solely on treating what comes out of the engine, there are at least as many gains to be had by reducing how many pollutants it produced in the first place. However, relying on a single approach to reduce one type of emission may cause an increase in others.

Instructions

1. Install an appropriately sized, three-way catalytic converter with oxygen injection. These converters are the hottest thing going today where emissions are concerned, and are the scrubber of choice wherever they may be used legally. Obtain a new, three-way converter designed for an engine like yours (with a similar displacement, horsepower/torque rating and operating range (rpm band)). Your donor vehicle should ideally be of about the same weight as the one into which you intend to install the converter.

2. Reprogram your computer or re-jet your carburetor to run slightly leaner than it did stock. Most computers and carburetors come from the factory set to deliver air to fuel at about a 14.0-14.7 to one ratio. Increasing this ratio to about 15.5 to one is safe for most engines, and will reduce the amount of unburned fuel that makes it out of your tailpipe.

3. Install a camshaft with less intake/exhaust overlap. Camshafts dictate how long your intake and exhaust valves stay open relative to crankshaft position. The intake and exhaust valves will typically stay open for about 200 to 210 degrees of the crankshaft's 360-degree rotation. Do the math and you'll find that both the intake and exhaust valves are both open at the same time for at least 40 degrees of crankshaft rotation. This allows unburned fuel to flow right from the open intake valve and out of the exhaust valve without getting burned. Install a shorter-duration camshaft with less overlap to reduce unburned hydrocarbon emissions.

4. Install a urea-injection system like those used on some modern diesel engines. Urea is an organic compound commonly found in mammalian urine, and is a powerful metabolizer of anything containing nitrogen. This includes the highly toxic Nitrogen oxide (NOx) emissions inherent to subjecting nitrogen and oxygen (the air is about 70 percent nitrogen by volume) to extremely high temperatures and pressures. This step is especially crucial if you've tuned your fuel system for a lean-burn, since numerically higher air/fuel ratios drastically increase cylinder temperature and subsequent NOx emissions.

Tips & Warnings

• Reducing vehicle emissions isn't all about treating combustion gases. Almost anything that you can do to increase fuel efficiency will net you gains in emissions produced per mile driven, as less fuel burned means fewer gases produced. Consider installing a high-flow catalytic converter back (cat-back) exhaust system, an electric cooling fan and a set of under-drive pulleys to reduce accessory drive speed. Dump your power steering in favor of a manual rack, and then fill the engine, transmission and gearbox with synthetic racing oil to reduce parasitic drag and subsequent power losses. Weight reduction, aerodynamic improvements and low rolling-resistance tires are all proven mileage improvers as well. Enhancements like these will help to increase your fuel economy and decrease every type of emission simultaneously without creating any new ones.

References

• Autoshop101: Emissions Sub-Systems - Catalytic Converter
• Family Car: Emissions Systems
• University of Brighton: The Effect of Compression Ratio on Exhaust Emissions from a PCCI Diesel Engine
• Autos.Msn: Diesels Going Green