Why no more lean burn??

[Randy]

Having EGR ports in the head instead of an external tube just means the engine was designed for EGR from the start. It's not really a Honda-specific thing... there are Hondas with an EGR tube, and the rather old Ford 351/400M engines have the EGR completely cast in head/intake.

[pgfpro]

Honda progressing with high-efficiency low-emission Homogeneous Lean Charge Spark Ignition (HLSI) combustion work
Honda is developing a Homogeneous Lean Charge Spark Ignition (HLSI) combustion engine as one of the key elements in its technology roadmap for a higher thermal efficiency gasoline engine. Honda reported on its basic approach in a 2013 SAE paper; Takashi Kondo of Honda R&D then presented results to date at the recent SAE 2014 High Efficiency IC Engine Symposium.

Lean burn engines using a stratified air-fuel configuration with a comparatively rich mixture in the vicinity of the spark plugs can deliver stable combustion of an overall lean mixture. Lean burn engines can deliver a higher theoretical thermal efficiency, and their higher air/fuel (A/F) ration leads to low pumping losses. However, because a comparatively rich mixture is burned during the first half of combustion, engine-out NOx emissions are not reduced sufficiently, and the emissions reduction provided by the three-way catalyst (TWC) is insufficient, Kondo noted.

Honda is striving to develop a form of lean burn with homogeneous premixture that would be able to balance low NOx emissions with stable, controllable combustion. The Honda HLSI approach seeks to take the best of conventional lean-burn (controllability and low combustion noise) and homogeneous charge compression ignition (HCCI) (ultra-Low NOx and high thermal efficiency) while avoiding the downsides of each: NOx emissions for the former and operating range, controllability and combustion noise for the latter.


LINK
Green Car Congress: Honda progressing with high-efficiency low-emission Homogeneous Lean Charge Spark Ignition (HLSI) combustion work

[serialk11r]

That looks good, but if you read the thing they say the trick is to get the mixture up to 1000K to get consistent burn, plus 50ppm NOx is too high (by a lot!). While getting the mixture up to 1000K is easier on 30:1 AFR, at idle that is going to be a huge challenge because you still have to run some manifold vacuum.

Though, with cooled EGR you could reduce the burn temperature a little more while still getting the mix up to 1000K if that is indeed a critical threshold for consistent combustion, but you'd lower the efficiency a bit with unburned fuel.

We should all hope that direct NOx catalysts become commercially feasible if we're going to hit those 2025 CAFE targets.

[serialk11r]

Originally Posted by Old Tele man

Did you also notice the more than DOUBLING of Unburned Fuel loss--from 2.8% up to 6.4%--on the Heat Balance chart?

Mazda was working on laser ignition plugs for the rotary engine, and I think when push comes to shove laser plugs might get widely adopted to squeeze out an extra 1% or whatever in fuel efficiency, because they don't take much space in the combustion chamber and can have multiple ignition points to reduce that unburned fuel loss. But if you're talking a lean burn engine, the multiple ignition points means the temperature will also go up slightly and you'll have more NOx to deal with.

[RustyLugNut]

Originally Posted by Old Tele man

Did you also notice the more than DOUBLING of Unburned Fuel loss--from 2.8% up to 6.4%--on the Heat Balance chart?

What's interesting is the huge reduction in Pumping Loss, from 3.1% down to only 0.9%.

Unburned fuel loss reductions can gain even more efficiency.

[RustyLugNut]

Originally Posted by serialk11r

That looks good, but if you read the thing they say the trick is to get the mixture up to 1000K to get consistent burn, plus 50ppm NOx is too high (by a lot!). While getting the mixture up to 1000K is easier on 30:1 AFR, at idle that is going to be a huge challenge because you still have to run some manifold vacuum.

Though, with cooled EGR you could reduce the burn temperature a little more while still getting the mix up to 1000K if that is indeed a critical threshold for consistent combustion, but you'd lower the efficiency a bit with unburned fuel.

We should all hope that direct NOx catalysts become commercially feasible if we're going to hit those 2025 CAFE targets.

And, while 1000k is a target number at ignition, compression heating and turbulence add to the energy meaning you do not need an intake temperature of 1000k.

NOx traps are already widespread in use.

[jeffcat]

Originally Posted by cbaber

There is a passage that runs from the exhaust ports towards the rear (transmission) side of the head. From there it goes to the electronically controlled EGR valve (M/T HX, CVT HX is vacuum controlled). The EGR is mounted on the intake manifold by the distributor. It goes from the EGR valve through maze like passages, located under the fuel rail on the intake manifold. There is a small passage leading into each cylinders intake runner.

For the 92-00 Civics, the HX and VX are the only trims that had EGR valves (at least for the US). 01+ I think all Honda's had EGR valves.

Are these pictures for the VX? I see the EGR valve on my VX and where it feeds into the intake but I don't see an "EGR runner chamber" like indicated on this picture and it's not on the Honda factory diagram either for the D15Z1.


If there is no way to take the EGR chamber apart? If not how do you clean the EGR ports running to each cylinder?....just take the entire intake off and set it in a solvent bath?

[ever_green]

I know I don't have a honda but I have been able to experiment with fairly lean mixtures of 1.3 lambda at higher RPMs which equate to 65-80 mph cruising with my Subaru (higher RPM because intake velocity is faster and the fuel atomizes properly in manifold). I haven't had any misfire issues. This is with EGR. The reason I can't go any leaner is because my wideband is restricted to 0.7-1.3 lambda and timing is already maxed out at 54* BTDC.

In any case other than larger than normal throttle opening during cruise I haven't really observed any noticeable gains in mileage. I know bosch research indicates that 15.6-16.8 AFR produces best BSFC but I don't want to go that rich because of extreme NOx emissions there. Even so I ended up reverting back to more normal 1.0 Lambda mixtures and enjoyed the better throttle response and cooler cylinder head temps (though hotter exhaust temp). Yeah the new stratified charge lean burn Hondas might help, but the new Prius can get pretty good mileage on highway without lean burn. Therefore I personally don't see the point. I mean the cost of new lean burn catalysts are staggering from what I have heard and I'm not sure Honda owners will be pleased when it comes to its service/replacement time.

[serialk11r]

Originally Posted by ever_green

Yeah the new stratified charge lean burn Hondas might help, but the new Prius can get pretty good mileage on highway without lean burn. Therefore I personally don't see the point.

Well, lean burn is better than cooled EGR like I mentioned for attaining complete combustion. Of course, the biggest problem is getting rid of the NOx, and the current NOx traps are not a good solution.

Since you've experimented with this, do you mind sharing your fueling tables? I'm thinking about getting a BRZ and I'm super excited to fiddle with the ECU (that is, lean burn!). Just to get an idea of how lean you can go at what speed.

[ever_green]

Originally Posted by serialk11r

Well, lean burn is better than cooled EGR like I mentioned for attaining complete combustion. Of course, the biggest problem is getting rid of the NOx, and the current NOx traps are not a good solution.

Since you've experimented with this, do you mind sharing your fueling tables? I'm thinking about getting a BRZ and I'm super excited to fiddle with the ECU (that is, lean burn!). Just to get an idea of how lean you can go at what speed.

Standard Subaru ecu does not allow you to go leaner than 14.68 Afr or lambda 1.0 in closed loop. What you have to do is induce a fulltime open loop behavior and then have the Maf sensor underestimate airflow by reduce Maf scaling. This is a lot of work as it requires you to reduce the engine load scale across the board in ecu or else it will think there is less cylinder pressure than actually is and run too much timing (this is just one example). Also on the BRZ I highly doubt this is feasible. The direct injection and firing angle tables are extremely confusing and I wouldn't dare tinker with it.