Spring 2008 Forward to a Friend

BY-PRODUCTS OF FUEL CHEMICALLY CHANGED TO HEAT ENERGY, EMISSIONS ARE KEPT UNDER TIGHT CONTROL BY TODAY’S SUBARU VEHICLES.
AUTOMOTIVE EMISSIONS ARE A HOT TOPIC. THEY’RE AT THE HEART OF CONVERSATIONS ABOUT EARTH’S OZONE LAYER, ALTERNATIVE FUELS, AND CONTEMPORARY AUTOMOTIVE TECHNOLOGY.

Subaru has implemented a number of designs and systems to help reduce emission ...

Every stage in the life of a vehicle produces emissions of one type or another. They are produced during manufacturing, utilization, maintenance, and disposal.

However, most people are concerned about emissions that result from an engine’s combustion process.

WHAT HAPPENS INSIDE AN ENGINE

During a gasoline engine’s four-stroke cycle, air is drawn into the cylinders with gasoline during intake, compressed, ignited, and pushed out through the exhaust system.1 That air is composed of nitrogen (79 percent), oxygen (20 percent), and inert gases (1 percent).

During complete combustion of gasoline (a hydrocarbon), oxygen joins with hydrogen to form water. Carbon joins with oxygen to form carbon dioxide (CO2).

Combustion is rarely complete. Contributing factors include uneven engine temperatures and impurities in the fuel. This results in hydrocarbons (HC) and carbon monoxide (CO) entering the exhaust system. Carbon monoxide is poisonous and, along with hydrocarbons, harmful to the atmosphere. The engine’s high pressure and temperatures greater than 2,500 degrees Fahrenheit produce oxides of nitrogen (NOX), which add to air pollution, acid rain, difficult breathing, and lung damage.

Subaru has implemented a number of designs and systems to help reduce emissions – so much so that some Subaru models have available Partial Zero Emission Vehicle (PZEV) engines.

CONTROL THROUGH EFFICIENT COMBUSTION

A Subaru vehicle reduces harmful emissions by burning fuel as efficiently as possible. Here are some of the components and systems that contribute2:

  • Electronic control of engine and transmission functions by microcomputer fine-tunes engine components to the variables of intake air and exhaust composition
  • Electronic Throttle Control precisely interprets driver input
  • Direct ignition eliminates wiring and enhances firing precision
  • Mass air, anti-knock, and other engine sensors contribute to precise operation while safeguarding engine components
  • Variable intake- and exhaust-valve timing enables a wider range of engine power and improved combustion
  • Intake systems promote the thorough mixture of air and fuel
  • Sequential multi-port fuel injection more precisely regulates fuel flow
  • Four valves per cylinder promote improved breathing to maximize combustion
  • Centrally located spark plugs in the cylinder heads help to maximize combustion
  • Reduced-friction designs of valve springs, piston rings, oil pumps, and other engine components promote power development and operating efficiency
  • Catalytic converters and O2 sensors help reduce harmful emissions in the exhaust system

CATALYTIC CONVERTER CONTROL WITHIN THE EXHAUST SYSTEM

As exhaust gases leave the engine through the exhaust system, catalytic converters help to reduce CO, HC, and NOx emissions. Converters look like small mufflers from the outside, but contain a ceramic honeycomb to which platinum, palladium, and/or rhodium have been fixed. The converter catalyzes the change from CO, HC, and NOx to CO2.

Catalytic converters don’t function properly until heated to approximately 600 degrees Fahrenheit. So when the vehicle is started, its control modules increase idle speed and raise shift points to help the engine warm up quicker.

CLEANER AIR

Subaru engines evolve from year to year. Small and large tweaks and modifications promote higher efficiency and improve emissions control. These measures provide a sharp contrast to the capabilities of engines in vehicles manufactured just a few decades ago.

This article is part of a series that will address the Subaru R1e electric cars now undergoing testing (see the Subaru News section) and Subaru PZEV engines. Watch for these stories in future issues of Drive.

Subaru engine components and systems are designed to keep emissions at low levels.
1 For more about the four-stroke cycle, see “Active Valve Control System (AVCS) – Timing Is Everything” in Winter 2005 Drive.
2 Not all are available on all models.
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Cautions for State Emission Testing

If your state requires emission testing, please be aware that full-time 4WD and AWD Subaru models must never be tested on a two-wheel dynamometer. Serious transmission damage could result.

For more information, see this Technical Alert at www.subaru.com.