106
Alternative Fuels for Transportation
results obtained by providing two different methods of diesel fuel and methanol engine supplied. The first method consists in the methanol admission
through a carburetor combined with the classic diesel fuel injection, and the
second one refers to the separate fuels injection. From the exhaust emissions
measurements, it was shown that the smoke and NO x levels significantly
reduced for all the engine loads with an increasing amount of methanol in
the blend.
For a diesel engine, fuel injection timing is a major parameter that affects
the combustion and exhaust emissions. The state of air into which the fuel
is injected changes as the injection timing is varied and, thus, ignition delay
will vary. If the injection starts earlier, the initial air temperature and pressure are lower; therefore, the ignition delay will increase. If the injection
starts later (when the piston is closer to TDC), the temperature and pressure
are initially slightly higher and a decrease in ignition delay results. Hence,
variation in injection timing has a strong effect on the engine performance
and exhaust emissions, because of changing the maximum pressure and
temperature in the engine cylinder. Therefore, Canakci, Sayin, and Gumus
(2008) investigated exhaust emissions of a single–cylinder diesel engine
under different injection timings when methanol-blended diesel fuel was
used. The tests were conducted at three different injection timings (15°, 20°,
and 25° CA BTDC). All tests were conducted at four different loads (5, 10, 15,
and 20 Nm) at constant engine speed of 2200 rpm. The following part summarizes the emission results of that study.
4.7.2.1 Carbon Monoxide (CO) Emissions
CO is a colorless, odorless, poisonous gas, and it must be restricted. CO
results from incomplete combustion of fuel and is emitted directly from
vehicle tailpipes. Besides the ideal combustion process that combines carbon (C) and oxygen (O 2 ) to CO 2 , incomplete combustion of carbon leads to
the formation of CO. The formation of CO takes place when the oxygen
present during combustion is insufficient to form CO 2 (Heywood 1984). In
general, while the engine is running under fuel-rich mixture conditions,
the exhaust will contain a large amount of CO emission, because there is
not sufficient oxygen to convert all of the carbon atoms of the fuel into CO 2 .
Thus, the most important parameters that affect CO emissions are an insufficient amount of air and an insufficient time in the cycle for complete combustion (Ganesan 1994).
Concerning the effect of different fuels on CO emissions, it was uncovered
that increasing the methanol ratio in the fuel–blend lessened CO emissions.
In comparison to M0, the change in CO emissions was around 19%, 32%, and
39% for M5, M10, and M15, respectively, at 5 Nm load and advanced injection timing, as demonstrated in Figure 4.12a. Methanol is an oxygenated fuel
and leads to more complete combustion; hence, CO emissions reduce in the
exhaust. CO emission decreased gradually when the engine load increased.
Alternative Fuels for Transportation
results obtained by providing two different methods of diesel fuel and methanol engine supplied. The first method consists in the methanol admission
through a carburetor combined with the classic diesel fuel injection, and the
second one refers to the separate fuels injection. From the exhaust emissions
measurements, it was shown that the smoke and NO x levels significantly
reduced for all the engine loads with an increasing amount of methanol in
the blend.
For a diesel engine, fuel injection timing is a major parameter that affects
the combustion and exhaust emissions. The state of air into which the fuel
is injected changes as the injection timing is varied and, thus, ignition delay
will vary. If the injection starts earlier, the initial air temperature and pressure are lower; therefore, the ignition delay will increase. If the injection
starts later (when the piston is closer to TDC), the temperature and pressure
are initially slightly higher and a decrease in ignition delay results. Hence,
variation in injection timing has a strong effect on the engine performance
and exhaust emissions, because of changing the maximum pressure and
temperature in the engine cylinder. Therefore, Canakci, Sayin, and Gumus
(2008) investigated exhaust emissions of a single–cylinder diesel engine
under different injection timings when methanol-blended diesel fuel was
used. The tests were conducted at three different injection timings (15°, 20°,
and 25° CA BTDC). All tests were conducted at four different loads (5, 10, 15,
and 20 Nm) at constant engine speed of 2200 rpm. The following part summarizes the emission results of that study.
4.7.2.1 Carbon Monoxide (CO) Emissions
CO is a colorless, odorless, poisonous gas, and it must be restricted. CO
results from incomplete combustion of fuel and is emitted directly from
vehicle tailpipes. Besides the ideal combustion process that combines carbon (C) and oxygen (O 2 ) to CO 2 , incomplete combustion of carbon leads to
the formation of CO. The formation of CO takes place when the oxygen
present during combustion is insufficient to form CO 2 (Heywood 1984). In
general, while the engine is running under fuel-rich mixture conditions,
the exhaust will contain a large amount of CO emission, because there is
not sufficient oxygen to convert all of the carbon atoms of the fuel into CO 2 .
Thus, the most important parameters that affect CO emissions are an insufficient amount of air and an insufficient time in the cycle for complete combustion (Ganesan 1994).
Concerning the effect of different fuels on CO emissions, it was uncovered
that increasing the methanol ratio in the fuel–blend lessened CO emissions.
In comparison to M0, the change in CO emissions was around 19%, 32%, and
39% for M5, M10, and M15, respectively, at 5 Nm load and advanced injection timing, as demonstrated in Figure 4.12a. Methanol is an oxygenated fuel
and leads to more complete combustion; hence, CO emissions reduce in the
exhaust. CO emission decreased gradually when the engine load increased.