Clean Automotive Technology...

Innovation that Works

Clean Diesel Combustion – Clean Diesel Combustion –

Clean, Efficient, and Cost Effective T Clean, Efficient, and Cost Effective Technology echnology

Diesel engines are used worldwide because they achieve better fuel economy, lower carbon dioxide

(CO2) emissions and produce higher levels of power than conventional gasoline engines. However,

diesel engines tend to be more costly and emit high levels of oxides of nitrogen (NOx) and particulate

matter (PM) emissions. While several technology options exist to decrease these emissions, the U.S.

Environmental Protection Agency (EPA) and industry partners are evaluating and developing EPA’s

Clean Diesel Combustion (CDC) technology , which refines several existing technologies into a unique

engine design that is simultaneously clean, efficient, and cost effective.

What is Clean Diesel Combustion?

The method of CDC encompasses a series of design

changes to the diesel engine, which decrease NOx

emissions while maintaining or improving engine

efficiency. The key concept of CDC technology is the

development of in-cylinder NOx control, where NOx

emissions are reduced in the engine combustion

chamber without penalizing the engine’s efficiency.

Preliminary EPA research has demonstrated positive

results for a design that achieves in-cylinder NOx

emissions much lower than levels reported by industry.

A clean diesel combustion engine with its various components.

0.20

0.19

0.18

0.17 0.16

0.18

0.19

0.18

0.15

0.14

0.16

This real engine test map shows that NOx emissions

are low over the entire engine operating map. Brake

mean effective pressure (BMEP) is a measure for

comparing performance of one engine to another.

Key Features of CDC Technology

• EPA Fuel System – Uses a hydraulically intensified fuel

system to lower PM and smoke emissions, and improve

engine efficiency.

• Boost System – Increases the engine power and the

efficiency of the combustion process, thus reducing

emissions and increasing fuel economy.

• Low Pressure Exhaust Gas Recirculation (EGR) – Lowers

the peak combustion temperature to reduce the formation

of NOx.

• PM Aftertreatment – Reduces the remaining smoke,

unburned hydrocarbons (HC) and carbon monoxide in the

exhaust to levels required for future emissions standards.
Clean A Clean Automotive T utomotive Technology...

Clean, efficient, cost-effective Clean, efficient, cost-effective

Technical challenges include lowering particulate emissions coming directly from the engine,

demonstrating the robustness of the technology in real world operation, and keeping cost/durability

relative to other approaches for meeting future stringent diesel emission standards. EPA continues to

improve the development of this technology by addressing these issues.

Benefits of CDC

CDC, with its unique combination of technology

advances, offers benefits such as:

• Low Cost – In-cylinder NOx control (where NOx

emissions are reduced in the engine combustion

chamber) greatly simplifies the aftertreatment

system requirements (conventional

aftertreatment to reduce smoke, PM, and HC).

• Low Emissions – Potential to achieve levels of

2007/2010 Heavy-Duty Engine and Tier 2

emission standards without the use of NOx

aftertreatment.

• Scalable – Applicable to both light-duty and

heavy-duty diesel engines.

Technology Advances to Achieve Emission Standard Levels

EPA emission standards – both 2007 heavy-duty engine and the Tier 2 standards for passenger vehicles –

call for major reductions (ranging from 77 to 95 percent) in NOx and PM emissions. Although several

methods are being examined to meet these future standards, today’s primary path option to reduce diesel

NOx emissions is through the use of aftertreatment devices. NOx aftertreatment devices control emissions

downstream from the engine’s combustion chamber, in the exhaust system rather than in the engine.

Research on CDC technology suggests that cost-effective

alternatives for long-term NOx compliance may not need to

rely exclusively on NOx aftertreatment methods. CDC

technology may be an attractive alternate method to achieve

future stringent diesel emissions standard levels.

Currently, EPA is actively discussing CDC technology with

potential partners to continue advancing the research and

possibly introduce the concept into production in the future.

EPA420-F-04-023

March 2004

43%

42%

38%

41%

39%

40%

This real engine test map shows a high level of engine

efficienty at various speeds and ooads. For this test, the

boost was externally supplied, simulating a well-matched

turbocharger (P exhaust = P input + 1.5 psi)

For model year 2007, NOx emission standards for heavyduty engines are reduced over 90% of current standards.