Method of determining fuel evaporation from an engine oil sump
A method of determining the total evaporation rate of fuel from an oil sump of an engine comprising: a) defining for said fuel, a plurality (n-1) of zones, each zone comprising a separate temperature range, and corresponding to a particular fuel constituent portion; b) determining or estimating the mass of said particular fuel constituent portion present in the sump for each zone; c) for each zone, determining an evaporation rate based on oil temperature; and the corresponding mass determined in step b); d) summing the evaporation rates for each zone from step c) to provide said total evaporation rate.
1. A method of determining the total evaporation rate of fuel from an oil sump of an engine, the method comprising:
a) defining for said fuel, a plurality (n-1) of zones, each zone comprising a separate temperature range, and corresponding to a particular fuel constituent portion, wherein each zone is assumed to correspond to chemical components which evaporate with the same evaporation rate;
b) determining or estimating the mass of said particular fuel constituent portion present in the sump for each zone;
c) for each zone and its corresponding fuel constituent portion, determining an evaporation rate based on oil temperature and the corresponding mass determined in step b);
d) summing the evaporation rates for each zone and its corresponding fuel constituent portion from step c) to provide said total evaporation rate; and
e) indicating a fault situation of the engine or controlling the engine dependent on the total evaporation rate determined from step d) or a parameter derived therefrom;
wherein in step a) the zones are selected such that the corresponding temperature ranges are such that the evaporation curve of the fuel is substantially linear within this range, which evaporation curve is a percentage of fuel evaporated against temperature.
2. A method as claimed in claim 1 wherein in step c) the determination of evaporation rates assumes that all chemical components of each fuel constituent portion evaporate with same evaporation rate.
3. A method as claimed in claim 1 wherein in step c) the evaporation rate for the zone is determined from the following equation:
m
Z
.
=
m
Z
a
Z
e
-
E
Z
RT
oil
where:
R is the gas constant (8.31 J·K −1 ·mol −1 );
T is the oil temperature (in K);
Ez is activation energy (in J·mol −1 ) with respect to that zone;
a is pre-exponential factor or frequency of collision (s −1 ) with respect to that zone; and
m z is the initial amount of fuel with respect to that zone z present in the oil sump.
4. A method as claimed in claim 1 including integrating the total evaporation rate with respect to time to determine the amount of fuel removed from the sump during a time period.
5. A method as claimed in claim 1 including determining the amount of fuel in an oil sump dependent from said determined amount of fuel removed.
6. A method as claimed in claim 5 including determining the amount of fuel in the oil sump dependent additionally on an initial amount of fuel present in an oil sump minus the amount of fuel removed.
7. A method as claimed in claim 5 including determining the amount of fuel in the oil sump dependent additionally on the amount of fuel entering the sump during cranking and/or warm up.