prototypes. Durability tests with these vehicles are continuing at the present time. In addition to work performed under contract to TACOM, Ford has conducted experiments involving this type of engine in passenger cars. Both four-cylinder and eight-cylinder engine conversions have been used. In addition, stratified-charge engine installations have been made on two commercial-type vehicles. It is evident from Table 3-10 that several of the vehicles under test in this program are capable of meeting the 1976 federal emission standards at low vehicle mileage.

One of the advantages of the stratified-charge engine is excellent fuel economy relative to conventional engines, particularly when emissions controls are applied. The original version of the stratifiedcharge L-141 engine developed for optimum fuel economy showed a 30 percent fuel economy gain over the conventional carbureted engine. However, as in a conventional engine, when EGR is used to reduce NO emissions, the fuel economy is reduced. With NO emissions at 0.33 grams per mile, the emissions-controlled stratified-charge engine fuel economy is comparable to that of the original L-141 conventional engine.

X

X

With less

EGR, at 0.7 grams per mile NO about a 10 percent fuel economy gain is 'x'

obtained.

3.9.2 Carbureted Stratified-Charge Engine

An alternative approach, the CVCC system, now being developed by Honda, achieves charge stratification with a prechamber and dual carburetor. The engine uses a conventional engine block, pistons, and spark plugs; only the cylinder head, intake and exhaust manifolds, and carburetor are modified. The cylinder head contains a small precombustion chamber in addition to the main combustion chamber. spark plug is located in the prechamber, which is fed through a separate carburetor and intake system with a fuel-rich mixture through a The main carburetor and intake system feeds a fuel

small third valve.

lean mixture to the normal intake valve.

The

The fuel-rich mixture ensures good ignition; the approximately stoichiometric mixture at the prechamber exit propagates the flame into the fuel-lean mixture in the main chamber. A slow-burning flame is

X

required to reduce NO formation and allow HC and CO burnup inside the engine. Emissions of NO, CO, and HC are all lower than those of a conventional engine at the same lean air-fuel ratios.

In February 1971, emissions data with this system on engine dynamometer tests indicated the engine could meet 1975 standards; the first successful car test that met the standards was in Spring 1972. In addition to developing a 2-liter, 4-cylinder engine for their own vehicle, Honda has applied the same techniques to modify two Chevrolet Vega 4-cylinder engines.

The Honda system is the most developed stratified-charge engine to date and has the lowest bare-engine emissions. Low-mileage emissions data are given in Table 3-11 for 54 Honda vehicles and two modified GM Vegas. All these cars met the 1975 standards without EGR or exhaust treatment, and Honda has expressed confidence that larger engines using the CVCC approach could also be made to meet 1975 standards without a catalyst. Especially impressive is the standard deviation of the lowmileage emissions of these vehicles. The standard deviation is 10 to 15 percent of the mean emissions. In comparison, mass-produced conventional-engine vehicles show standard deviations of 30 percent of the mean at higher emission levels.

Three Honda cars have completed 50,000-mile durability testing and met the 1975 standards with ease at every 4,000 miles. Data for these tests are given in Table 3-12. The Federal Test Procedure 11-lap mode was followed in these tests. Maintenance required was minor.

In a recent series of three tests at low mileage, the average emissions measured were 0.25 grams per mile HC, 2.5 grams per mile CO,

Data for this table current on November 24, 1972

Data for this table were current on November 24, 1972.