Attachment E
- 4

Definition of Similar Engines

As stated in the Audit Protocol at Paragraph s I.B.2.a.v , emissions measured from an engine that has been stack

- tested (a “Stack

- Tested” engine) may be used to determine the emissions from an engine that has not been stack

- tested (a “Non

- Stack

- Tested “ engine) if the Non

- Stack

- Tested engine is deter mined to be similar to the Stack

- Tested engine. A Stack

- Tested engine is one that has been (1) tested using any of the methods set out in the Audit Protocol at Paragraphs I.B.2.a.v , or (2) subject to emission tests by its manufacturer or for wh ich the manufacturer has provided reliable emissions data.

Definition of “s imilar ” A Non

- Stack

- Tested engine may be considered similar to a Stack

- Tested engine if its emissions of a particular pollutant are expected to be no greater than such emissions fr om the Stack

- Tested engine , based on the criteria in the table below

. EPA developed the concept of similarity for use in Clean Air Act programs that require manufacturers to certify that their engines comply with federal emissions standards. EPA desc ribed the concept in the nonroad engine certification program. That program specifies how similar engines are combined into groups known as engine families (see 40 CFR Parts 89.116, 90.116, and 1048.230). An engine manufacturer uses a single engine model and rating to certify emissions for an entire family of nonroad engines, even though individual engine ratings and applications may vary significantly. Because nonroad generator engines and stationary generator engines share basic technology, the methods used to identify groups of engines in nonroad applications also serve as a suitable foundation for establishing groups of engines in stationary applications. The methods that EPA established for nonroad engine certification are now specified in the new s ource performance standards for stationary spark

- ignition and compression

- ignition engines (see 40 CFR 60, Subparts IIII and JJJJ).
For purposes of the Audit Protocol, the criteria for determining engine similarity are included in the following table. These criteria, which include fuel selection, method of aspiration, cooling mechanism, fuel delivery system, and cylinder displacement volume , among others, are key characteristics that are specified in the nonroad engine certification program. Accordingly, a Non

- Stack

- Tested engine would be deemed similar to a Stack

- Tested engine if all of the statements in the right

- hand column are true and there are no ad ditional engine characteristics, such as ignition timing , operating cycle , engine controls, or emissions devices that indicate that the comparison would not be technically justified. Additionally, a Non

- Stack

- Tested engine can be determined to be similar to a Stack

- Tested engine when one or more of the statements in the right

- hand column are false, if it can be shown that the difference in characteristics can be expected to have little or no impact on emissions , with any justification being documented in t he final audit report.Criterion Stack

- Tested Engine Non

- Stack

- Tested Engine

Type of fuel consumed Diesel Same (i.e., diesel) Gasoline Same (i.e., gasoline) Natural gas Same (i.e. , natural gas) Kerosene Same (i.e. , kerosene) Other Same Method of air aspiration Natural aspiration Same (i.e. , natural aspiration) Turbocharged Same (i.e. , t urbocharged ) Cooling mechanism Water

- cooled Same (i.e. , water

- cooled ) Air

- cooled Same (i.e. , air

- cooled ) Cylinder displacement volume Any Same or lower displacement volume than tested engine ( within

- 1 0 % of tested engine volume ) Combustion chamber configuration (e.g., round v. “hemi”) Any Same (i.e, both engines have a round, “hemi,” or other shaped combustion chamber)

Combustion chamber / fuel delivery system design Direct injection Either direct injection or common rail injection

Common rail injection Either direct injection or common rail injection
Indirect injection Same (i.e. , indirect injection ) Carbureted fuel Same (i.e. , carbureted fuel ) Cycle Two

- stroke Same (i.e. , two stroke ) Four stroke Same (i.e. , four stroke ) Combustion timing Any Same (i.e., either set by manufacturer or similarly adjusted) Other relevant criteria (e.g., ignition timing, operating cycle , engine co ntrols, aftertreatment devices, exhaust gas recirculation ) Any Same (e.g., both engines are electronically controlled; both engines lack aftertreatment devices or the Non

- Stack

- Tested Engine has a device at least as effective as the Stack

- Tested Engine)