Development of the Second Generation Methanol Lean Burn System 892060
The second generation methanol lean burn system has been developed. The power unit is a new, 4 valve 1.6L in-line four with compact combustion chambers. Lean misfire limit was extended by using a swirl control valve in the intake port which improves combustion under partial load. Lean mixture control is made by using a signal from lean mixture sensor provided in the exhaust manifold. An EGR system has been newly adopted to reduce NOx emissions and a under-floor type catalyst is also used to reduce formaldehyde emission in the cold transient mode in addition to the manifold type catalyst.
Permissible excess air ratio range (PEXARR) was defined and used to indicate the potential for reducing vehicle NOx emissions in engine dynamometer tests to optimize compression ratio, valve timing and swirl ratio and to evaluate the effect of the EGR.
Test results indicate 0.4g/mile NOx at low mileage, and about 11% better fuel economy than stoichiometric feed back under FTP (Federal Test Procedure) driving cycle. The optimized second generation vehicle has an inertia weight of 2750 lbs. which is 500 lbs. heavier than the first generation one. The driveability is still in need of improvement. Although low formaldehyde emission was obtained at low mileage using this system, further study on the stability of this level during mileage accumulation is necessary.