Retrofit Technology
TRICYCLES
The tricycle consists of a motorcycle with an attached side car and comes in a variety of distinctively-customized configurations, shapes and sizes. Some configurations are unique to a neighborhood or geographic region, and others are simply branded by the individual owner. The Philippine tricycle has become as much a sign of personal expression as it has a symbol of national identity. It is a testament to the ingenuity and work ethic of the Philippine people.
Throughout the Philippines, the tricycle is consistently the most common mode of transportation - leading experts estimate that nearly 84% of the countrys population depends on the tricycle transport sector. Of the ~1.5 million registered tricycles in the Philippines, approximately 70% have two-stroke engines. In many Philippine cities, emissions from tricycles are the primary cause of air pollution, contributing to a multitude of related environmental, health and economic problems.
CONVENTIONAL DIRTY TWO-STROKE ENGINES
Carbureted two-stroke engines are typically used as the power source for "two-wheelers" (i.e. motorcycles, mopeds, etc.) and "three-wheelers" such as tricycles and tuk-tuks across Southeast Asia. The main reasons for this are: 1). their rugged yet simple construction, and 2.) their low cost and 3.) their high power-to-weight ratio. Unfortunately, two-stroke cycle engines are also characterized by high levels of unburned hydrocarbons, carbon monoxide, and particulate emissions.
The high hydrocarbon emissions from carbureted two-stroke engines result from the scavenging process used. Scavenging refers to the process by which the burned exhaust gasses are flushed from the engine. In a conventional "carbureted" two-stroke engine the fuel is entrained in the intake air stream before the combustion air enters the crankcase. The charge is compressed in the crankcase by the underside of the piston, and enters the cylinder when the piston uncovers the transfer ports. Combustion products from the previous cycle are forced or "scavenged" from the cylinder with this new air/fuel charge. Unfortunately, the exhaust ports are also open at this time, allowing 30%-40% of the fuel to be lost directly into the exhaust stream. At idle conditions the losses can be as high as 70%.
The high carbon monoxide emissions result from rich air to fuel ratio typically seen in these engines. High residual gas fractions within the cylinder lead to an environment in which consistent ignition is difficult. In order to improve combustion stability rich air fuel mixtures are typically used. This excess of fuel leads to incomplete combustion and high carbon monoxide levels.
Finally, the high particulate emissions result from the unstable combustion, excessive lubrication (typical in small two stroke engines), and a lubrication system which allows lubricating oil to be dissolved in the fuel. In a typical 2-stroke, the oil mixes with the fuel at the carburetor. As the air/fuel/oil mixture transfers into the crankcase, the fuel dissolves the oil. This action reduces the amount of oil deposited on the cylinder wall (or other critical components) as it is essentially washed out of the engine by the fuel.
30-40%
of the fuel in a conventional dirty Two-Stroke engine is lost directly in the exhaust stream without being burned.