What is a Speed Density0 engine managment scheme? Speed Density0 systems calculate the amount of air entering a motor using sensors that monitor engine operating conditions. The Ideal Gas Law0 (PV = nRT) is the basis for this type of engine management. Instead of directly measuring the amount of air entering the motor ("n" in the above equation), speed-density systems estimate it using n = PV / RT, and then applying additional corrections. Fuel tables in a honda ECU0 (from a theoretical standpoint) are Volumetric Efficiency (VE) tables. Basic operation:

• A Map Sensor0 is used to measure the pressure of air in the intake manifold (DENSITY term in speed-density). This provides the P term in the Ideal Gas Law0 calulation.
• The engine's rotational speed (SPEED term in speed-density) is used to estimate the volume of air entering the motor by multiplying how much air is sucked into the cylinder each stroke (usually displacement divide by two) by the number of engine revolutions. This provides the V term in the Ideal Gas Law0 calculation.
• The Intake Air Temperature Sensor0 measures the temperature of air entering the engine, providing the T term in the Ideal Gas Law0 calculation.
• R is a constant
• Knowing P, V, R and T, the ECU0 can then calculate an estimate of n (moles of air entering motor) from sensor data and n = PV / RT

Because speed-density calculates airflow instead of directly measuring it, additional factors are often used to provide a better estimate. The TPS Sensor0 is key in many of these - TPS tip-in enrichment is used to provide more fuel that the Ideal Gas Law0 calculation suggests in order to provide fueling for a rush of new air prior to the Map Sensor0 reaching a steady state. Off-throttle leaning is used to prevent the motor running rich after sudden decreases in throttle. Here are some links to more information about speed-density systems: - http://web.archive.org/web/20081203203734/http://web.archive.org/web/20081203203734/http://www.asashop.org/autoinc/jan97/techtotech.htm0 - decent link, not TOO techy.

• http://web.archive.org/web/20070205103708/http://www.wincom.net:80/trog/efi.html0 - quite technical but practically oriented
• http://www.simcar.com/literature/sae940759/sae940759.htm0 - highly technical paper on practical use of speed density systems for air/fuel management. Has excellent figures illustrating the role of secondary correction factors, like TPS accel/decel.
• One0 [Two](http://web.archive.org/web/20040825011344/http://baen.tamu.edu:80/users/lepori/Teaching/BSEN265/Lectures/ICEng_Power_Eff0. PPT) Three0 [Four](http://web.archive.org/web/20050913080557/http://baen.tamu.edu:80/users/lepori/Teaching/BSEN265/Lectures/Engine_cycles0. PPT) Five0 Microsoft Powerpoint presentations from a College Engineering class on gas laws, thermodynamics and engines.