Small internal combustion reciprocating engines (ie. Less than 50cc displacement) are one of the major power plants for portable power generators, small power equipment (ie. Lawnmower) and transportation across the globe (especially in developing regions).

As such, they are also a substantial contributor to global air pollutants. They currently produce more than 5% of the total man-made hydrocarbon emissions that contribute to ozone formation. In some regions of the U.S. the lawn-mowers using small engines are responsible for 13% of unburned hydrocarbon emission. Yet very few standards exist to regulate the emissions from these small engines.

Based on the type of ignition, internal combustion engines are classified as either spark ignition engines (SI) or compression ignition engines (CI). A newer operating mode for internal combustion engines called homogeneous charge compression ignition (HCCI) can lead to an increase in fuel efficiency and a reduction of emissions (particularly NOx) when compared to engines under SI or CI operation. Until recently, however, most applications and research efforts in HCCI operation have been focused on passenger cars and light trucks with engines that are 2L or larger in displacement.

Very little research has been conducted on the potential of smaller scale HCCI engines. Thus, further study in HCCI operation in small scale engine may improve the fuel efficiency and emission in an area where regulation is not yet stringent.

Goal and Objectives

The purpose of this project is to create a small scooter engine testbed that can be used to refine small engines in order to improve their efficiency and to reduce their production of harmful emissions.

Objectives

• Design and develop a chassis support structure for the scooter and dyno system
• Re-wire, organize and prep engine to instrument with sensors
• Develop LabView code for data acquisition
• Design and produce automatic throttle control
• Collect engine performance data under HCCI

Innovation

HCCI
• Novel combustion concepts being explored for high-efficiency, low pollutant emission engines are based on strategies for achieving LowTemperature Combustion (LTC). LTC requires the formation of reacting mixtures in an engine that are dilute enough to not produce the high temperatures that lead to NOx and that have well-enough mixed fuel and air to avoid soot formation.
• Traditional SI gasoline engines and CI diesel engines have to operate at unfavorable combinations of temperature and fuel-air ratios for the formation of NOx, and in the case of Diesels, soot.
The simplest form under which LTC operations can be realized is homogeneous charge compression ignition (HCCI) operation.
• This engine offers the opportunity to achieve high thermodynamic efficiency and sharply or completely eliminate production of soot and oxides of nitrogen (NOx). It accomplishes the low NOx emissions by operating at very low product temperatures.

How it works
• A four stroke HCCI engine may be thought of as a CI and SI engine combined into one
• During the intake stroke a uniform (homogeneous) mixture of air and fuel enters the combustion chamber.
• The compression stroke gives enough energy input to the charge, so that the temperature reaches an autoignition condition for the fuel. This combustion process occurs without help from a spark plug.
• Due to the homogeneous nature of the charge and by running at very low fuel/air equivalence ratios ignition begins at many points simultaneously and occurs at a significantly lower temperature because there is no flame propagation.

The Bigger Picture